OVDAS-SERNAGEOMIN reported that during 3-15 April activity at Villarrica gradually declined after a minor seismic crisis on 3 April, though bursts of seismicity concentrated SE of the main crater suggested possible magma movement at depth. The Alert Level remained at Yellow (the second lowest level on a four-color scale) and the public was warned to stay outside of a 1-km radius around the crater.

Lava lake reappears in February 2015 and is ongoing; large ash explosion on 3 March 2015

Villarrica is a stratovolcano located 675 km S of Santiago, Chile. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently visible lava lake with Strombolian activity was responsible for persistent MODIS thermal anomalies between November 2009 and April 2012. Very little additional activity was observed until December 2014, when renewed activity was reported by the Southern Andes Volcano Observatory, (Observatorio Volcanológico de Los Andes del Sur, OVDAS) part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), a privately funded research group that studies Villarrica.

Increased fumarolic and thermal activity was first observed in early December 2014 followed by Strombolian activity and ash emissions during 4-6 February 2015. A large explosion with an ash plume to 9 km altitude took place on 3 March 2015, and continued moderate explosive and Strombolian activity occurred a number of times during March. Explosive activity with ash plumes and lava spattering continued at decreasing levels throughout 2015; in 2016, minor ash emissions were only reported in September. Intermittent Strombolian activity at the lava lake occurred throughout 2015 and 2016 and was recorded as significant thermal anomalies through October 2016.

Activity during 2014. OVDAS reported that seismic activity in 2014 started the year very low with 604 total events in January. Steam plumes remained below 500 m above the summit throughout the year except for one report of heights to 800 m in February. Tremor displacements in 2014 remained in the range of 0.4 to 1.2 cm2 at frequencies of 1.1-1.2 Hz and amplitudes of 0.6-0.7 μm/s, all within background levels. Sulfur dioxide emission values ranged between 180 and 566 metric tons per day (t/d) as monthly averages, with maximum values not over 1,600 t/d throughout the year. The number of seismic events increased from 1,160 in April to 3,269 in May 2014, and took a larger jump between June and July from 4,268 to 11,031. The number of monthly seismic events remained in the 10,000-12,000 range through 2014, while the other parameters measured by OVDAS remained stable. There were no reported ash emissions.

As a privately funded research group, POVI documents activity at the volcano with webcams, photographs, and frequent summit ascents. They first observed increased sulfurous fumarolic activity on 25 November 2014. They also reported on NASA ASTER IR observations of a progressive increase in spectral brightness in satellite data on 10 and 26 November and 3 December. POVI observed the presence of particulate matter suspended over Villarrica on 9 December, and a light dusting of material within 1,000 m of the summit the following day. Increased acoustic activity of loud explosions of gases inside the 40-m-wide volcanic vent at the summit crater were reported during 10-12 December.

OVDAS reported on 18 December 2014 that the seismic energy had abruptly declined on 9 December. A flyover by the Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), the National Emergency Office of the Ministry of Interior and Public Safety, on 17 December was not able to observe the bottom of the crater due to weather conditions. In January 2015 seismic activity returned to previous levels and other measurements remained at background levels.

Activity during 2015. On 4 and 5 February 2015 POVI observed the first Strombolian eruptions inside of the summit crater vent since April 2012, and constant strong degassing occurring in 10 minute pulses. On 6 February they captured nighttime images of incandescent explosions rising to 65 m above the crater edge. Spatter fragments up to 40 cm were scattered around the summit. POVI also recorded two ash explosions on 6 February, and photographed 5 m diameter incandescent blocks on 7 February in the air 45 m above the crater.

A gradual increase in the amplitude of the seismic tremor signal was reported by OVDAS beginning on 6 February. The seismic signal rose from DR (Reduced Displacement) values of 4.0 cm2 to 24 cm2, and amplitudes increased to 18.5 μm/s, considered moderate to high for Villarrica and significantly above its background values of 2 cm2 and 1 μm/s. The location of the tremor signal was also shallower than it had been previously.

During the night of 9-10 February, POVI observed about 24 Strombolian explosions that rose above the crater rim and sent large blocks several meters down the NW flank. MODVOLC thermal anomalies pixels first reappeared on 14 February 2015. Between 14 and 16 February two active lava lakes were observed by POVI within the summit crater in nighttime imagery and during a flyover. OVDAS reported up to five explosions per minute at the summit crater on 16 February and continued nighttime incandescence since 6 February accompanied by intermittent ash emissions. Ejecta on 16 February was observed up to 1 km away on the S flank. Temperatures close to 800°C were measured that day near the lava lake surface on a flyover supported by ONEMI; tephra was observed around the crater rim and a thin layer of ash was distributed on the flanks. This caused SERNAGEOMIN to raise the alert level from Green to Yellow (1 to 2) on a 4-level scale.

A further increase in seismic energy release was reported by OVDAS on 28 February 2015 with DR values increased to 35 cm2, along with observations of nighttime incandescence and Strombolian explosions ejecting tephra up to 1 km from the crater. Two days later SERNAGEOMIN raised the alert level to Orange (3 of 4) based on increased DR values close to 80 cm2 and seismic amplitudes of 40 μm/s, as well as increased Strombolian activity and bombs ejected to 500-600 m from the crater.

An explosion early in the morning of 3 March 2015 with a 3-km-high ash plume, DR values near 400 cm2, and seismic amplitudes of 1,400 μm/s prompted SERNAGEOMIN to raise the alert level to Red (4 of 4) that morning. They reported observations from cameras around the volcano of a 1.5-km-tall lava fountain (figure 30). The Buenos Aires VAAC (Volcanic Ash Advisory Center) reported a plume to 9.1 km altitude drifting ESE later in the day. Significant ashfall was also visible around the flanks shortly after the explosion (figure 31).

Figure 30. Explosive eruption at Villarrica on 3 March 2015, photographed from the city of Villarrica, 30 km NW of the volcano. The lava fountain was reported as 1.5 km tall. Courtesy of POVI.

Figure 31. Ground-based webcam and satellite views of Villarrica before and after the 3 March 2015 eruption. The ash plume drifted E and spread ash on the glaciers around the N and E flanks of the volcano. The explosion sent ejecta radially outwards generating small lahars in drainages to the north and east. Images A and B courtesy of POVI (copyright by Mario Alarcon N.) from a camera located in Pucón, 17 km N. Images C and D annotated by POVI; courtesy of NASA Earth Observatory.

The alert level was lowered back to Orange (3 of 4) on 6 March 2015 as activity decreased. During a flyover on 9 March, OVDAS scientists observed that the vent inside the crater was partially obstructed with debris, and fumarolic activity was weak. Minor debris avalanches had significantly decreased and the alert level was lowered to Yellow (2 of 4) on 10 March. A minor ash emission, under 100 m above the crater, occurred on 15 March. Two weak Strombolian explosions to 150 m above the crater were reported by OVDAS on 17 March. During 17-18 March, continued explosions with volcanic bombs, incandescence, and fine ash caused SERNAGEOMIN to raise the alert level back to Orange. POVI observed ash drifting E less than 70 m above the crater during this time.

The Buenos Aires VAAC reported water vapor and light ash emissions to 3 km beginning 22 March, drifting 45 km SE and continuing intermittently through 25 March. OVDAS reported sporadic incandescence throughout this time and intermittent ash plumes generally 100-500 m above the crater. POVI had also noted pulsating emissions of fine ash during 18-25 March. A significant increase in activity on 25 March led to a 700-m-high plume with high ash content, and visible incandescence. A flyover by OVDAS/ONEMI that day confirmed the presence of the lava lake near the surface again with temperatures around 1,000°C. The Buenos Aires VAAC reported a 5.5-km-high ash plume on 27 March extending 55 km NE. Plume heights exceeded 800 m on 28 March, with ejecta from the lava lake landing around the summit and upper flanks, and night incandescence. Strombolian explosions were observed for most of the night on 30 March. The highest explosion of spatter reached 300 m above the crater, and material fell 500 m away onto the flanks. That same day the Buenos Aires VAAC reported continuous ash emissions with a plume to 3.7 km drifting NE. On 31 March they reported irregular intermittent water vapor with small puffs of ash that were observed on the OVDAS web camera.

Strombolian activity fluctuated during April 2015. Pulsating emissions of water vapor were common. OVDAS reported ash plumes to 700 m above the summit crater on 4-5 and 20-21 April but otherwise periodic ash plumes were below 500 m. Buenos Aires VAAC reported the 5 April ash plume rising to 3.7 km altitude and drifting 16 km SSE. Ejecta occasionally reached 200 m from the crater. Nighttime incandescence from the crater was usually observed during clear weather, and seismicity generally decreased during the month. The lava lake and the formation of an incipient pyroclastic cone inside the inner crater were observed in an OVDAS/ONEMI flyover on 9 April; on a 21 April flight moderate Strombolian activity was viewed restricted to the interior of the crater.

During May 2015, OVDAS reported small Strombolian explosions from the lava lake, diffuse gas emissions with occasional ash, nighttime crater incandescence, and decreasing seismicity. Activity continued to gradually decline, and on 8 June the Alert Level was lowered to Yellow.

Sporadic incandescence was still observed during clear weather between June and September 2015, with plume heights below 450 m except for occasional plumes to 700 m above the summit crater. Two ash emissions were recorded on the OVDAS cameras on 18 and 21 September to heights less than 400 m. Plume heights in October were near 700 m, and another small ash emission was recorded on 31 October along with incandescence on clear nights. A group of OVDAS scientists conducted a field visit on 27 October and observed 11 new small fumaroles on the inner wall of the crater, and steep walls of pyroclastic material generated in the explosions from earlier in the year. They observed the lava lake in an overflight on 29 October and the temperature of the lake was measured at 850°C (figure 32). During the second week of November weak explosions were heard and pyroclastic material was observed above the crater rim; plume heights were close to 400 m, but rose to 700 m in December. A particulate emission that rose to 200 m above the crater occurred on 15 December. SERNAGEOMIN lowered the alert level to Green on 31 December 2015.

Although ash emissions and Strombolian activity were intermittent and generally decreasing after June 2015, strong thermal anomalies seen in MODVOLC data continued throughout the year. February, March, July, August, October, and November each had between 5 and 10 days with thermal anomalies while April, May, June, September, and December all had between 10 and 15 days with MODVOLC alert pixels, indicating continued activity at the lava lake.

Activity during 2016. Water vapor plumes rose to 600 m above the crater in January and February 2016, along with slightly increased SO2 emissions and night incandescence. Small ash emissions on 6 and 29 February and the formation of a small pyroclastic cone inside the crater were observed by visiting scientists from the University of Cambridge. One VT (volcano-tectonic) earthquake of M 3.7, larger than normal, was reported by OVDAS on 26 March; it was located 4.7 km ESE of the crater at a depth of 4.2 km. This was followed by a spike in the number of VT events the following day. The amplitude and frequency values associated with seismic tremors remained within normal levels until a sudden but brief increase on 3 April that was associated with explosions and minor Strombolian activity at the lava lake within the crater. This activity resulted in SERNAGEOMIN raising the alert level to Yellow. The frequency of clusters of VT seismic events increased during the second week in April; most were located in a NW-SE trending belt about 10 km long near the crater vent. Water vapor plumes continued rising to around 600-700 m above the crater during April and May with no significant changes in incandescence. OVDAS reported small emissions of particulate material around the crater in April and on 4 May. The alert level was lowered back to Green on 16 May.

From May through July 2016, only water vapor plumes between 300 and 700 m above the summit were reported by OVDAS. August was quieter still with plumes rising to only 150 m. Seismicity increased slightly in September, plumes rose to 600 m, and on four days (5, 10, 19, 24) small emissions of ash were observed. Water vapor plumes remained below 700 m in October, 2016.

While significant explosive activity did not occur during the year through October 2016, the lava lake remained visible and active, causing thermal anomalies recorded by MODIS and measured by both the MODVOLC and MIROVA systems. MODVOLC recorded thermal anomalies between 5 and 10 times each month from January through April, between 1 and 4 times in May, July, and August, and again between 5 and 10 times in September and October. This variation is also reflected in the MIROVA Log Radiation Power graph for 2016 (figure 33).

Figure 33. MIROVA system Log Radiative Power data for Villarrica between 8 November 2015 and 8 November 2016. The thermal anomalies were continuous and consistent except for a quiet period between late May and early August 2016. Courtesy of MIROVA.

OVDAS-SERNAGEOMIN reported that during 3-15 April activity at Villarrica gradually declined after a minor seismic crisis on 3 April, though bursts of seismicity concentrated SE of the main crater suggested possible magma movement at depth. The Alert Level remained at Yellow (the second lowest level on a four-color scale) and the public was warned to stay outside of a 1-km radius around the crater.

OVDAS-SERNAGEOMIN reported that at 0750 on 3 April the seismic stations at Villarrica began recording more energetic volcanic tremor. In addition, the webcam recorded increased surficial activity characterized by Strombolian explosions and intensifying crater incandescence. The Alert Level was raised to Yellow (the second lowest level on a four-color scale) and the public was warned to stay outside of a 1-km radius around the crater and away from drainages.

On 8 June, OVDAS-SERNAGEOMIN reported that activity at Villarrica continued the gradual decline observed in recent weeks. The Alert Level was lowered to Yellow (the second lowest level on a four-color scale) and the public was warned to stay outside of a 3-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported no significant changes at Villarrica during 27 May-2 June. Seismicity fluctuated at low-to-moderate levels, and continued to indicate small explosions and degassing from the lava lake. Deformation data suggested minor inflation. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and 200 m away from drainages in the SW and NE quadrants.

OVDAS-SERNAGEOMIN reported no significant changes at Villarrica during 20-26 May. Seismicity had significantly decreased, although the data continued to indicate small explosions and degassing from the lava lake. Deformation data suggested inflation during 24-26 May. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported no significant changes at Villarrica during 6-12 May. Activity was characterized by weak and infrequent Strombolian explosions from the lava lake, diffuse gas emissions with occasional ash, nighttime crater incandescence, and decreasing seismicity. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported moderate seismic activity during 29 April-5 May. Nighttime crater incandescence and a thermal anomaly detected daily in satellite images suggested an active lava lake, with mild and periodic Strombolian activity. Gas emissions were visible in the daytime. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported that during 15-28 April seismicity at Villarrica fluctuated but remained at moderate levels. Intermittent crater incandescence was observed and diffuse gas plumes mostly consisting of water vapor rose from the crater. Data from monitoring stations and pictures taken during an overflight on 21 April confirmed the presence of a lava lake and Strombolian explosions. During 23-27 April Strombolian explosions ejected material that remained mostly within the crater or no more than 100 m away. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and 200 m away from drainages.

OVDAS-SERNAGEOMIN reported that infrasound data indicated explosions at Villarrica on 8 April. The next day seismicity increased and acoustic signals suggested discontinuous Strombolian activity and an oscillating lava lake in the crater. Gas emissions and nighttime incandescence from the crater were observed; this activity continued through 14 April. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported that during 31 March-4 April small Strombolian explosions at Villarrica continued, and seismicity slightly and steadily increased. During 4-5 April pulsating emissions of water vapor and ash rose 700 m above the crater. Strombolian explosions sometimes ejected material outside the crater, onto the flanks, at distances no greater than 200 m. Pulsating gas-and-ash emissions continued at a lower level during 6-7 April. Nighttime incandescence from the crater was occasionally observed, and seismicity decreased. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported that during 24-25 March gas-and-ash emissions at Villarrica decreased but the magnitude of the continuous seismic tremor slightly increased. Crater incandescence overnight was observed. By the evening of 25 March Strombolian activity was confined to the crater and a gas plume rose 700 m above the crater rim. Seismicity fluctuated but increase overall. The lava lake had returned and was about 1,000 degrees Celsius. During 26-27 March Strombolian activity ejected tephra out of the crater to distances of about 500 m, and a gas plume rose more than 800 m. During an overflight on 27 March scientists noted that material which measured 1,110 degree Celsius originated from two vents. During 28-31 March a gas-and-ash plume rose from the crater and Strombolian explosions ejected tephra from the crater; several explosions starting at 2200 on 30 March, and continuing the next morning, ejected tephra 300 m above the crater and as far as 500 m from the crater onto the flanks. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages.

OVDAS-SERNAGEOMIN reported that at night on 17 March explosions at Villarrica ejected tephra onto the flanks and produced nighttime incandescence. Pulsating ash plumes rose 300 m and drifted E. Seismicity increased and was characterized by low-magnitude tremor. The Alert Level was raised to Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages. During 19-22 March pulsating plumes recorded by the webcam had a greater concentration of ash, and rose 100-500 m and drifted NE. Moderate levels of tremor were detected. Although cloud cover often prevented observations of the crater, incandescence was occasionally seen at night. During 22-24 March continued gas-and-ash emissions rose 400-500 m and drifted SW; the plumes were less dense, shorter, and contained less ash content. Incandescent material continued to be ejected from the crater, but with less frequency, and was deposited near the crater on the NE flank.

Based on OVDAS-SERNAGEOMIN data, representatives from ONEMI, SERNAGEOMIN, Sistema Nacional de Protección Civil, and others reduced the exclusion zone around Villarrica to 5 km on 5 March. OVDAS-SERNAGEOMIN reported that the Alert Level for Villarrica was lowered to Orange (the second highest level on a four-color scale) on 6 March, citing that seismicity had declined to below baseline levels and visual observations indicated no active lava lake. During an overflight on 9 March scientists observed subsidence of material in the crater which partially obscured the conduit. Weak degassing was also noted. On 10 March the Alert Level was lowered to Yellow; OVDAS-SERNAGEOMIN warned of avalanches of unconsolidated material and maintained an exclusion zone of 3 km.

OVDAS-SERNAGEOMIN reported that on 28 February a significant increase in seismicity at Villarrica was detected along with Strombolian explosions and tephra ejected 1 km away. Seismicity continued to increase and on 2 March indicated that the lava lake level had risen. Strombolian explosions continued and ejected tephra as far as 600 m onto the flanks. Seismicity again increased significantly at 0230 on 3 March. The Alert Level was raised to Red (the highest level on a four-color scale). Strombolian activity intensified and became continuous, ejecting a large volume of material onto the flanks and producing a 1.5-km-tall lava fountain. Lava flows descended the flanks. The eruptive plume rose 6-8 km above the crater and drifted 400 km ENE. According to ONEMI about 3,600 people were evacuated from a 10-km-radius of the volcano. At 1500 ONEMI reported that seismicity was decreasing, and by 1800 was low. Only weak pulses of ash rose from the crater, and most evacuees had returned home.

OVDAS-SERNAGEOMIN reported that activity significantly increased at Villarrica during 1-16 February, characterized by increased seismicity, crater incandescence, and explosions. On 6 February seismicity increased significantly, explosions occurred in the crater, and ash emissions rose above the crater rim. The Alert Level was raised to Yellow (the second lowest level on a four-color scale). DOAS (Differential Optical Absorption Spectrometry) data showed an average monthly sulfur dioxide emission value of 222 tons per day; a high value during this period of 450 tons per day was recorded on 11 February. The highest number of explosions, five per minute, during the period occurred on 16 February. Explosions ejected incandescent material out of the crater as far as 1 km onto the S flank. During an overflight on 16 February, supported by ONEMI, volcanologists observed the lava lake and recorded temperatures near 800 degrees Celsius, tephra in and around the active crater, and a diffuse layer of ash on the flanks.

Projecto Observación Visual Volcán Villarrica (POVI) reported that at night during 4-5 February faint incandescence was detected with a near-infrared camera. On 5 February Strombolian explosions ejected tephra several hundred meters high. On 6 February tephra was ejected about 65 m above the crater rim and two consecutive ash emissions were observed. OVDAS-SERNAGEOMIN reported that the Alert Level for Villarrica was raised to Yellow (the second lowest level on a four-color scale) due to the increased seismicity, indicating a fluctuating lava lake and small explosions. Scientists noted a rise in the lava-lake level during an overflight. POVI reported that on the morning of 7 February bombs were ejected from the crater, some almost 5 m in diameter. Later that day the intensity of the explosions decreased and crater incandescence became irregular.

According to Projecto Observación Visual Volcán Villarrica (POVI), satellite images of Villarrica acquired on 10 and 26 November and 3 December revealed a progressively more intense thermal anomaly. Photographs on 9 December showed particulates suspended above the crater rim, and the next day a thin veneer of ash covered the NW edge of the crater rim. Detonations from the crater were heard during 10-12 December. On 13 December observers noted that the intense blasts of gas from the previous few days had removed some ash deposits from the inner crater wall leaving lighter colored streaks.

According to Projecto Observación Visual Volcán Villarrica (POVI), satellite images of Villarrica acquired on 25 July revealed a weak thermal anomaly. On 29 July observers photographed the crater and described a thermal anomaly on the S edge of the crater rim, in the same area from which a lava flow originated on 29 December 1971. They also heard deep degassing sounds. A second photograph showed a diffuse gas plume rising from the bottom of the crater, and ash and lapilli on the snow on the inner crater walls.

According to Projecto Observación Visual Volcán Villarrica (POVI), images of Villarrica posted on 14 November showed a dense plume rising and obscuring the deeper parts of the crater, and an area on the W part of the crater rim with ash and bomb deposits.

According to Projecto Observación Visual Volcán Villarrica (POVI), incandescence from Villarrica's crater subsided mid-April and was undetected by satellite and ground observations at least through 10 November. Images captured by a camera in Pucon (16 km N) on 10 November showed an increase in the plume intensity. Small water vapor plumes, 50 m wide, rose from the depths of the crater.

According to Projecto Observación Visual Volcán Villarrica (POVI), two small ash emissions from Villarrica occurred on 7 March. Incandescence from the crater was observed from the town of Pucon (16 km N) during 7-8 March.

According to Projecto Observación Visual Volcán Villarrica (POVI), an image from 17 September showed the inner SSW wall of the crater covered with snow and ice, and a thin layer of ash. A rapid rise in the level of the lava lake (in a pit about 40 m wide) on 19 September caused much of the snow and ice to melt, especially on the southern inner wall. Strombolian explosions from the crater were observed on 26 September, and tephra deposits on the E edge of the crater were noted. On 27 September incandescence from the lava lake were reflected in the cloud cover above.

Based on Significant Meteorological Information (SIGMET) advisories and web camera views, the Buenos Aires VAAC reported that during 1-2 November ash plumes from Villarrica rose to altitudes of 3.7-4.6 km (12,000-15,000 ft) a.s.l. and drifted N, NE, E, and ESE. Ash was not detected on satellite imagery. On 2 November a steam-and-gas plume drifted NE.

On 12 May, OVDAS-SERNAGEOMIN reported that a slight increase in activity from Villarrica during April led to a change in the Alert Level from Green Level 1 to Green Level 2. April's activity was characterized by increased seismicity, a rise in the lava lake level, more vigorous fumarolic activity, and more frequent incandescence at night. According to the Projecto Observación Visual Volcán Villarrica (POVI), the spattering lava lake was about 100 m below the crater rim on 10 May.

OVDAS-SERNAGEOMIN reported that during February incandescence from Villarrica was seen at night through web cameras. The report reiterated that incandescence was typical; the Alert level remained at Green, Level 1. Video and photographs taken during 24-25 April, and posted on the Projecto Observación Visual Volcán Villarrica (POVI) website, showed Strombolian activity in the crater. Bursts of lava ejected from an unseen source did not rise above the crater rim. Gas plumes rose from the crater.

Based on web camera views, the Buenos Aires VAAC indicated that on 11 March a diffuse gas-and-ash plume from Villarrica drifted near the crater. Ash was not detected on satellite imagery. That same day, SERNAGEOMIN reported that, during an overflight, scientists saw a typical-looking gas plume drifting SW and tephra deposits on the flanks.

SERNAGEOMIN reported that on 26 October three gray plumes with little ash content were emitted from Villarrica and rose to an altitude of 3.2 km (10,500 ft) a.s.l. The plumes quickly dispersed to the E. About 20 minutes later a darker gray plume rose to an altitude of 3.3 km (10,800 ft) a.s.l. Projecto Observación Visual Volcán Villarrica (POVI) reported that the latter plume deposited a thin layer of tephra several kilometers in length on the E flank.

According to a news report, the Oficina Nacional de Emergencia reported that unusual seismicity was recorded at Villarrica during early April. Fresh ash deposits were seen outside of the volcano's crater. Visitors were banned from climbing the volcano.

During visits to Villarrica's summit in September observers saw incandescence until the 28th. On the 28th deep sounds emanated from the volcano every 1-2 minutes and lapilli deposits were seen on the crater's edges. On 16 October incandescence was not visible and strong, deep noises were heard every 7-10 minutes.

Observations of Villarrica on 9 April revealed that no incandescence or explosive noises occurred in the volcano's crater. A lava lake, whose surface was 200 m below the crater rim, was last seen at the volcano on 19 January. At that time explosions at Villarrica occurred every 5-10 minutes.

On 9, 16, 17, and 21 August volcanic ballistic clasts were observed falling near the WSW edge of the crater. In addition, observations of the volcano on 22 August revealed that the lava lake had risen 40 m since 9 August.

Volcanic activity at Villarrica was at relatively normal levels as of 9 August. The amount of incandescent lava decreased in comparison to the amount observed during 19 and 22 July. Strong degassing occurred and ejections of ash, lapilli, and volcanic bombs landed on the W to SW edge of the crater.

Villarrica is a strato volcano located on the border of the provinces of Cautin and Valdivia, southeast of the lake and town of Villarrica. The crater is almost circular, with a diameter of about 200 m and a depth of 300-400 m.

The Villarrica volcano began its acitivity on 29 October with a weak gas explosion and sparse pyroclastic material. On 29 November it became active again and ejected lava flows and pyroclastic cone in its central crater. The activity intensified between 3 and 20 December, characterized by three basaltic lava flows on the southwest slope of the volcano. The flows descended from the central crater up to the base of the central cone near the Villarrica somma, at an altitude of approximately 2,000 m. The lava flows caused partial melting of the cover ice and slowly formed a channel in the glacier with a depth between 20 and 40 m. There were lava flows with pyroclastic emissions every 30 seconds in the central crater. In the slope in front of the lava flow there were three dense columns of water vapor produced by the slow glacier fussion. Emergency zones are maintained in the valleys of the Vaipir, Chaillupen, and Conaripe Rivers.

It is important to remember that in the last eruption (3 March 1964) the Villarrica Volcano extruded a lahar flow near the village of Conaripe and caused the deaths of 25 persons. In the present eruption there has been material damage and the affected zone is absolutely controlled.

February 1972 (CSLP 95-71)

"An eruption began at midnight 29/30 December. Volcanic ash was ejected and blown in a southeasterly direction by a moderate wind. The ash eruption ceased at about 12 o'clock 30 December. The top of the volcano changed its form, showing now a deep notch. Simultaneously with the explosive activity, lava flows left the volcano and went down the northern and southern sides. Melting water of the ice cover produced avalanches of a mixture of water, sand and boulders which reached the inhabited valleys at about 0130 in the morning of 30 December. Several bridges were broken, a lot of houses destroyed, and about 30 persons died. A lava flow going down on the southern side nearly reached the Calafquen Lake. The rock is a basalt with about 5% olivine and 15% plagioclase phenocrysts. It may be interesting that during to whole month of January in southern Chile high seismic activity has been recorded."

After a long period of fumarolic activity, a series of explosions that began on 19 September at 2200 ejected ash from the main crater. The next morning, a long, dark-colored pyroclastic flow could be seen on the NW flank. On 24 September at 0800 fine ash was ejected briefly, covering Villarrica's snowy slopes.

"Forest guards in the Villarrica National Park reported that the volcano entered into a remarkable eruptive stage on 14 October, after a long period of moderate activity. Continuous explosions with tephra emissions and some black pyroclastic flows over the ice-covered slopes have been observed. By night, a red glow over the summit indicates that a lava fountain is filling the crater. Since the big lava and pyroclastic eruptions of October-December 1971, active fumaroles have been present in the main crater."

"A brief eruption from Villarrica's central crater was reported during the afternoon of 11 August. After three strong explosions and underground rumbling, a dark ash column was seen rising more than 200 m above the summit. Winds blew the ash over the snow-covered SE flank. Seismometers operated by the Universidad de la Frontera at Temuco (100 km NW of the volcano) recorded an increase in seismicity during the event."

The first paragraph is from a report from Oscar González-Ferrán. The quoted material is from a report from Hugo Moreno, Leopoldo López Escobar, Pedro Riffo A., and Gustavo Fuentealba.

Villarrica began to erupt on 30 October. Activity was generally similar to that of the 1971-72 eruption. A very fluid basaltic lava column ascended the central crater without the emission of pyroclastics. Gases escaped freely, generating explosions in the crater that ejected lava spatter to 20-100 m in height, forming a spatter cone. Lava flowed NE from the base of this cone over the snow and ice that cover the upper flanks, excavating a channel and generating a large column of vapor. The Emergency Office took preventive measures to protect the population against possible avalanches. As of mid-November, the level of lava in the central crater continued to rise.

"On 30 October at 1745, authorities 16 km N of the summit (in Pucón) reported that explosions were occurring in the central crater and a small lava flow was pouring out from the NNE side of the crater through a small V-shaped opening left by the 1971 fissure eruption. The lava moved across the ice, quenched, and generated an avalanche mixed with ice and snow that reached 5 km from the summit (phase 1, figure 1).

Figure 1. Sketch map of the summit area and N flank of Villarrica on 30 October and 3, 13, and 18 November 1984. Courtesy of Hugo Moreno.

"Lava was emitted continuously from the central crater, advancing toward the NNE, where it melted the ice cover and formed a channel that was estimated to be 30-40 m deep, 50 m wide, and 1 km long during aerial observations 2-3 November. The central crater was occupied by a small flat spatter cone showing weak Strombolian activity. Lava from a small lake at the NNE foot of the spatter cone poured into the ice channel. Over the flat bottom of the channel, formed by solidified black lava, two narrow red lava flows were observed. Voluminous quantities of water vapor emerged from the area where the lava flow front was in contact with the channel's steep ice wall. Numerous fissures were present in the ice surrounding the channel, and on 3 November the ice cover on the SW flank also showed several deep fissures (phase 2, figure 1).

"There were no signs of eruptive activity 6-9 November, although tremors and underground rumbling were reported at Pucón. Strombolian activity at the small spatter cone in the central crater resumed 10-12 November, and lava flowed NNE into the ice channel. The speed of the flow was estimated at 10 m/s.

"As of midday on 13 November, almost 2 x 106 m3 of lava had flowed into the ice channel, most of which was concentrated at the lava front under the ice cover. At 1350 on the 13th, the lava front emerged onto the surface, generating a 3 km-long avalanche of lava blocks, ice, and snow, and leaving behind a 150 m-long ice bridge. Since only a very small mudflow moved downstream, it seems that most of the water generated by melting of the ice evaporated. New fissures were observed on the ice-covered SW, E, and NE flanks (phase 3, figure 1).

"Eruptive activity decreased 14-17 November, with only weak fumarolic emissions seen at the spatter cone and water vapor emission at the ice bridge. [Earthquakes] were reported 13 km E and 10 km SW of the volcano (at Palguin and Chaillupen).

"On 18 November, a clear deformation of the SW slope was observed between 2,200 and 2,800 m above sea level. Weak lava production from the central crater opened a new small ice channel, about 200 m long and 50 m wide, toward the N (phase 4, figure 1).

"Villarrica's October-November eruptive behavior is quite similar to the 1971 eruptive cycle that ended in a big lava effusion (29 December at 2345). Villarrica last erupted 11 August and during the first week in September, with small explosions and tephra emissions."

Between 16 November and 1 December, activity remained constant. The lava column maintained its pressure and level in the central crater, and there were small explosions and gas emissions. Strombolian activity increased 1-6 December. Tephra was ejected to about 100 m height every 10 minutes. Lava from the lake in the central crater continued to pour out slowly through the initial NE flank channel.

On 6 December between 1200 and 1500 there was a violent increase in the rate of lava production. Lava flowed out through a new channel NE toward the Río Correntoso (which turns NW and flows about 20 km into Lake Villarrica), reaching the base of the volcano. The activity generated a small lahar that flattened a small wooden bridge and affected houses beside the river. The volume of water returned to its normal level after 24 hours. An overflight of the crater revealed that the level of the lava lake was higher than before and the pyroclastic cone had grown higher than the central crater rim. Intense Strombolian activity continued 7-10 December. Pyroclastic material was ejected to 50-100 m height. Very liquid lava continued to pour out of the crater to the NE. Activity decreased gradually 11-19 December. Small explosions occurred 20 December but the pyroclastic cone and lava lake collapsed and effusive activity ended.

Explosive activity resumed 12 January between 1015 and 2300. A column of pyroclastics reached about 400 m height. A sequence of explosions ejected incandescent material to 100 m. On 18 January, the pyroclastic cone and lava lake in the central crater had completely collapsed.

"When the last eruptive cycle of Villarrica Volcano (30 October-26 February) began to decay in January 1985, seismic activity also decreased. Between January and June 1985, the seismograph located on the N flank of the volcano recorded a monthly average of 15 volcanic earthquakes (Minakami's B-type). In February, only five seismic events were recorded with very little harmonic tremor. However, since June 1985 volcano-seismic activity has increased significantly. At the same time, notable harmonic tremor was observed. Figure 2 shows monthly seismic activity between January and November 1985. This situation was continuing as of 25 November, with a small gap in mid-late November. On 19 November at 0700, harmonic tremor stopped abruptly, and only apparently very shallow seismic activity was recorded. On 21 November at 1000, harmonic tremor activity resumed.

Figure 2. Number of earthquakes per month at Villarrica, January-November 1985. Courtesy of Gustavo Fuentealba C.

"According to personal observations and reports from Pucón, a town at the N foot of the volcano, an increase in fumarolic activity and lava fountaining with weak explosions and very small ash emissions have been registered since April. A red glow has been seen at night since late September."

October 1988 (Ref 1988)

Lava lake activity

Boris Behncke reports that lava lake activity was observed at Villarrica in October 1988, by a student from Rühr Univ, Bochum. The summit crater, ~ 150 m deep, included a small cone that contained a vigorously bubbling lava pool roughly 50 m in diameter. Spatter was occasionally ejected above the crater rim. The lava lake activity had apparently been continuing since the end of the more vigorous 1984-85 eruptive activity.

An increase in fumarolic activity and weak explosions were observed in the crater during August-September. On 26 August, water in a nearby river (Río Carmelito) was cloudy and the river level abnormally high. Four days later, on 30 August, small ash emissions and continuous explosions were observed from 1430 to 1500, followed by a strong explosion at 1506. A weak emission of gray ash and a white gas plume 1 km high were observed on 17 September. Seismicity was at normal levels for the volcano.

Seismicity was recorded at the volcano during March-May by a telemetered seismic station (VNV) 4.5 km from the summit, at 1,400 m elev. The average tremor frequency decreased slightly from 1.9 Hz (in March-April) to 1.8 Hz (in May). Tremor frequency also decreased with distance from the summit. Average frequencies of 1.9, 0.8, and 0.6 Hz were recorded 4.5 km (station VNV), 18.7 km (station PP) and 21 km (station PL) from the volcano, respectively, in April. Since 28 May, activity has increased, and both tremor and volcanic earthquakes have been recorded.

Phreatic explosions 300-400 m high were observed from a town 15 km from the volcano every two minutes beginning at 1350 on 11 September. Fumarolic activity was intense. Activity decreased on 14 September. Seismicity was recorded earlier this year during March-May.

Explosions began on 3 November at 1640. Sebastián Moraga, a forest guard at Villarrica National Park, felt ~ 240 explosions in the next 3 hours. At 1940, a vigorous explosion ejected ash, which fell on a 200 x 250-m area on the NW flank. At the same time, the telemetering seismic station (operated by the Univ de la Frontera) 4.5 km from the crater recorded a strong increase in seismicity. The next day at 1326, a new explosion was felt by the forest guard. A plume drifted toward the SW that afternoon.

Tourists reported two new small pyroclastic cones on 6 November. The cones exhibited intense explosive activity and underground noises. Ash deposits were visible on NW-flank snow on 9 November. Clouds obscured the volcano on 10 November, but a portable seismograph (in Lican Ray) and a flank telemetric station recorded an increase in tremor amplitude and frequency.

Jeff Witter climbed Villarrica on 17 November and observed summit-crater activity for about an hour. The circular main crater, ~ 200 m in diameter and 100 m deep, had vertical sides and a flat floor covered by black spatter. Gas flux was vigorous and continuous from an incandescent pit, 5 m in diameter, ~ 20 m E of the center of the crater. At intervals of ~5-10 minutes, roughly 2 m3 of spatter were ejected from the pit to 15 m height. Sounds similar to ocean waves also emanated from the pit. After about 30 minutes of observations, a 2 m2 section of the crater floor collapsed, enlarging the pit. Five more glowing pits, none more than 0.5 m across, were visible along the E edge of the crater floor. No tephra was found on the surface of snow and ice in the summit area, although convection carried small scoria fragments to as much as 130 m above the crater floor.

Moderate fumarolic activity occurred from a 20 x 10 m area on the SW rim, and from a 10-m vent ~ 5 m N of the main crater rim. Gases were strong-smelling and caused a burning sensation in the eyes, nose, and lungs. Fumarolic activity appeared stronger the next day, when observations from the entrance to Villarrica National Park (~ 7 km away) revealed a white billowing vapor cloud enveloping the entire summit area.

The telemetered seismic station located 4 km NW of the main crater at 1,400 m elev recorded 11 high-frequency events (A-type) in June, compared to 3 in May, 1 in April, and 1 in March. Since March, ~ 25,000 tremor episodes have been recorded; ~ 6,000-7,000/month.

Beginning about 0730 in the morning of 26 September residents of the Centro de Ski Villarrica-Pucón (a ski resort) saw "scrolls of black vapor" emitted about once each minute from the main crater of Villarrica volcano. Vapor rose ~500-750 m above the summit. . . . Four such small explosions took place in the morning, the last, at 1100, coincided with a strong tremor felt at the ski resort.

Figure 3 shows the ash distribution seen by aerial observers in the upper part of the ski area (Piedra Blanca). The distribution was composed of thin ash chiefly visible due to the contrast with the white snow. One part of the ash distribution was bounded by a SE-trending band of heavier deposition. This ash fall deposit extended over 8 km, visible to the east as far as the limit of contrasting background snow.

Later on 26 September, between 2030 and 2130, observers saw incandescence above the crater that they attributed to glowing lava in the crater reflected in the fumarolic column. The next day (27 September) was partly cloud-covered, but strong fumarolic activity formed low-lying scrolls directed toward the E. Later, during a clearing in the clouds, observers saw a 500-m-long ash fall layer extending W.

Several seismic stations were installed on 26 September. Although two seismic stations were installed farther from the summit, it was not until 1630 that the station closest to the summit was installed near the Rio Voipir (at the 500-m contour, 13.5 km E of Villarrica). The record there showed continuous harmonic tremor along with other seismic events until about 2110. After that, and until 0600 on 27 September, tremor fell abruptly; however, three long-period volcanic earthquakes occurred in this interval. At 0700 harmonic tremor returned.

Starting at both 0741 and 0800 similar seismic sequences consisted of early events followed by a later event. The same sequence repeated about every 4 hours until the last one ended at 1000 on 28 September. The 4-hour sequence was interpreted as magmatic injections leading to gas-charged explosions. Thus, the main part of the eruptive episode lasted ~3.5 hours (0730-1100 on 26 September). It produced a magmatic eruption with a VEI of 1. The seismic signature associated with frequent gas-charged explosions was not previously seen at this volcano.

Between 25 and 30 December the volcano discharged continuously. At 1000 on 25 December 1994 personnel of Villarrica National Park saw "a small scroll of dark vapor." The plume was estimated as <250 m tall and prevailing winds carried it toward the SE.

The next day at 0815 park rangers noticed a second plume, dark brown to black in color ultimately rising to about 600 m above the summit. Winds again carried this plume SE.

Informants reported that on 29 December they could detect a thin layer of gray ash discoloring all of the snow-covered SE sector of the volcano. They also saw a dark gray stain trending N 120° E reaching at least 6 km (to the Portezuelo Chinay area). That same day, Villarrica discharged gas at 20-30 second intervals that looked grayish to sky blue, apparently rich in SO2. Occasionally light gray to brown drab discharges were also noticed and tentatively interpreted as minor gaseous explosions with a fine-grained ash component.

On 30 December at 0800 and 1100, the volcano produced dense plumes of dark gray to dark brown color. These reached up to 250 m above the crater where they were carried to the SE. After noon a weather front crossed the region and the escaping gases condensed as a great mass and slid down the SE flank. No discharges were specifically reported after this event.

Seismic monitoring began at 1807 on 26 December using a portable MEQ-800 seismograph installed 13.5 km from the principal crater.

During the next few days, tremor was seen; it typically had an amplitude of 2 mm and fundamental frequencies 0.8 Hz. During the first 4 hours of operation, 20-30 second intervals of tremor occurred ~60 times/hour. The next day (27 December) tremor increased to 120 times/hour. Starting at 1700 on 28 December tremor increased still further and it reached higher frequency, up to 1.1 Hz. On 29 and 30 December tremor remained essentially constant in terms of amplitude and duration, but after 0100 on 31 December, intervals of tremor took place more often, an average of 200 times/hour (i.e. 200 distinct intervals of tremor an hour). The number of tremor intervals an hour remained constant until 2100 (31 December) when tremor dropped to the levels seen on 29 and 30 December.

The tremor on 26 and 30 December was similar to that seen routinely during times of repose. Nevertheless, some lower frequency events (~2 Hz) took place coincident with weak ash eruptions. As of 31 December 1994 no new activity was reported.

Sketches of both the crater and ash lobes from late-December eruptions

Geologists who made an overflight of the stratovolcano late on the morning of 15 February (in conjunction with Simon Young and John Simmons) observed increasing fumarolic activity. Villarrica gave off moderate puffs of bluish, sulfurous gases at 1-2 minute intervals that rose 300-400 m above the crater before dispersing to the SE.

Between 1040 and 1245 on 15 February the local seismic station (VVN) registered an average of 3 tremor episodes per minute. This tremor had frequencies of 1.3-1.5 Hz, 0.3 Hz below the frequency customarily received (1.8 Hz), and considered a possible indication of a slightly deeper source than typical for both the tremor and the puffs. This behavior continued until 1900 on 15 February. Afterwards tremor diminished and puffing ceased at the fumaroles. These later conditions prevailed until at least 19 February.

The crater, a little more than 200 m in diameter, contained a nested terrace (figure 4). The inner crater floor sat ~200 m below the crater rim, the bottom 50 m of which was black in color, possibly composed of scoria. At the very bottom center an opening exposed ~20 m of material with a bright red glow.

Figure 4. Sketch of Villarrica's crater as seen on 15 February 1995. Courtesy of J. Naranjo, G. Fuentealba, and P. Peña.

Black ash on the glaciers of the E and S flanks extended 4.6 km in the S20 E direction and 2.5 km in the S direction (figure 5). These ash lobes could correspond to eruptions on 25 and 29 December 1994 (19:12).

Figure 5. Distribution of black ash from Villarrica's crater as seen on 15 February 1995. Courtesy of J. Naranjo, G. Fuentealba, and P. Peña.

Gustavo Fuentealba contributed the following on 4 May. "Seismic activity has increased in the past few days compared to March. In mid-April explosions were visible to the level of the crater rim and these explosions coincided with seismicity registered on portable instruments 15 km from the crater. The seismic signals arrived at 90-second intervals.

"In agreement with mid-April explosions and seismic data, aerial observations and photos around that time (taken by members of the Corporacion Nacional Forestal) revealed the growth of a new pyroclastic cone. Starting on 28 April and 1 May, there were intervals of poor visibility, but a new increase in seismic activity included tremor at 30-second intervals. Seismic activity declined suddenly, starting about 1915 on 1 May, but it reappeared ~8 hours later with tremor at 60-second intervals. Although continued poor visibility thwarted direct observations, it was thought probable that the April pyroclastic cone had collapsed."

Seismicity at Villarrica stratovolcano increased above background starting on 7 September. The seismic data lacked significant high-frequency response. This increase preceded ash emissions that took place about a week later. The events were recorded at the digital seismic station named "VNV" located on Villarrica at 1,500 m elevation; data is telemetered to the Universidad de la Frontera in Temuco.

At 1330-1335 on 14 September personnel of Chile's Programa Riesgo Volcánico (PRV) saw emissions of gas and ash generated by four rhythmic explosions. The resulting ash blanket covered 60,000 m2 and bordered the volcano's ski resort ("Ski Villarrica"), which lies ~4 km from the summit on the NW flank. Later, at 1427, a lower intensity gas emission was observed from the resort. No further emissions were seen. The eruptions were thought to have been due to degassing from shallow depth.

Above-background seismicity started on 7 September (BGVN 21:08); a follow-up report indicated that Villarrica's microseismicity again increased starting on 26 September and was continuing as late as 3 October. The events seen were of short-duration with dominant frequencies of 1.75 Hz and they appeared in swarms (figure 6). Some isolated events occurred in the 0.7-1 Hz range. In this same time interval the crater was the scene of abundant to occasionally intense degassing.

Figure 6. One of Villarrica's ongoing swarms of long-period seismic events (station VVN), 0900 to 0927 (GMT) on 26 September 1996. Reference marks are at one minute intervals. Courtesy of Gustavo Fuentealba and Paola Peña.

Crater observations for the interval 11 September 1996-13 January 1997

The following summarizes observations of eruptive activity during 11 September 1996-13 January 1997, based on descriptions by volcano guides and a visit to the volcano by Werner Keller in January 1997.

On 11 September 1996 a group of mountain climbers observed intense degassing of water vapor and reported that the small lava pond on the crater floor was not visible. On 14 September (BGVN 21:09) there was emission of ash accompanied by a dull rumbling noise. Guide Claudio Marticorena of Pucon was close to the summit with a group of tourists at the time of the ash emissions and reported that lava blocks tens of centimeters in diameter were ejected above the rim of the summit crater.

October and November were characterized by a notable rise of the magma column within the central crater pit, which was almost completely filled to its rim. Mountain guides Victor Sepulveda and Claudio Marticorena reported a vigorously convecting lava lake 50 m in diameter with fountaining from several areas of the lake. Frequent bursts ejected spatter and incandescent bombs beyond the summit crater, onto the upper flanks of the cone every few seconds. This activity lasted until mid-November 1996, followed by a rapid subsidence of the magmatic column and accompanied by strong vapor emission later that month. In December, the characteristic nocturnal crater glow observed at Villarrica during the past years disappeared.

Fumarolic emissions from the summit crater diminished in early January 1997, and on 4 January Sepulveda noted that the inner crater pit was again completely visible, for the first time since late November 1996. At that date, the central pit was ~100 m deep, with two small degassing vents at the bottom. No incandescent lava was visible in either of the vents, but gas emissions produced a distinct noise. The S part of the intracrater platform left after the 1984-85 eruption had collapsed into the central pit. On 13 January, mountain guides noted incandescent lava within the central pit: this suggested a new rise of the magma column.

In October and November 1996, activity was characterized by a rapidly convecting lava lake that nearly filled the central crater pit (BGVN 21:12). Fountains were noted on the lake's surface and frequent bursts ejected spatter and incandescent bombs beyond the summit crater. In December, the magmatic column subsided and the characteristic nocturnal crater glow disappeared. During the first two weeks of January 1997, incandescent lava returned to the central pit (BGVN 21:12). The following summarizes observations made from mid- January through mid-March by volcano guides Victor Sepulveda and Lorena Morales and documentary film makers.

The volcano guides reported that between 15 and 19 January few observations of the crater were made because of strong fumarolic activity. On 21 January a clear view revealed that the crater was unchanged since 13 January (BGVN 21:12). That day two small ash emissions from the summit crater were seen from Pucon, ~ 17 km N. The cause of these emissions may have been a landslide in the E crater, detected on 27 January. On 3 February, the crater floor was partially covered with talus, but a small vent was actively degassing in the N part of the crater floor. Another significant collapse of the NE crater wall occurred sometime before 15 February. By 17 February, two vents on the NE side of the crater floor had small Strombolian eruptions and extruded incandescent lava onto the crater floor. On 22 February, small lava fountains on the NE side of the crater floor were actively filling the crater with lava.

On 24 February, the guides reported that the crater floor had risen by several meters and convection was occurring within the lava pond. The film crew noted that two red spots in the crater produced irregular Strombolian activity, gas emissions, and strong noises. The film crew also reported that strong sulfur emissions required them to wear gas masks while at the summit and that these emissions appeared to be extruded from vents at the ash-covered icefields on the upper terrace in the crater (figure 7, number 1).

During late February the film crew reported seeing a light red glow at night above Villarrica's summit crater. These reports were confirmed by the volcano guides report of residents in Pucon seeing the glow on 2 March following several months of absence.

The documentary film crew took a summit overflight on 2 March and reported a change in crater morphology due to the collapse of the S terrace (figure 7, number 2). When they returned to the summit on 5 March there were no further morphological changes in the crater and degassing appeared the same as on 24 February.

On 12 March, the volcano guides observed a light dusting of ash that covered the NE flank of the volcano. Strombolian explosions from a vent on the crater floor continued throughout the remainder of March.

As reported by volcano guides on 17 February, two vents on the NE side of the crater floor had small Strombolian eruptions and extruded incandescent lava onto the crater floor (BGVN 22:04). On 24 February the guides reported that the crater floor had risen by several meters. Residents of Pucon (~17 km N) noted night glow on 2 March following several months of absence. Weak Strombolian explosions continued throughout the remainder of March.

The following describes visual observations made from April through August 1997 by members of the Villarrica Observation Project/Internet (POI) from Pucon. Table 2 presents observations since mid-October 1996.

Table 2. Summary of activity observed at Villarrica during October 1996 through August 1997. Courtesy of Werner Keller.

The lava pond in the crater interior continued with small Strombolian eruptions throughout April 1997 and could be observed during clear nights as a red glow above the summit crater. The parallel fumarolic activity was moderate and mainly consisted of vapor. In May the activity of the lava pond increased considerably with respect to degassing intensity and frequency. At night incandescent bombs could be seen every 5 minutes. On 22, 23, 24, 30, and 31 May small ash clouds were regularly emitted to ~200 m above the summit.

In June, due to the beginning of winter, few observations of the summit could be executed. Nevertheless short periods of clear weather made possible a view of the activity level of the crater indicating small Strombolian explosions every 2 minutes. On 10 July observers realized that the red nocturnal glow had disappeared, hinting at subsidence of the magma column. Between 17 and 19 July the summit showed no more signs of fumarolic activity. On 22 July small fumarolic emissions were registered again. On 31 July weak night glow reappeared over the summit after an absence of 21 days.

On 19 August the glow reached the same intensity as in June. The crater did not show any explosive activity, indicating slow uplift of basaltic lava with low gas contents. Observers confirmed that the magma column had subsided again on 25 August for the second time this year and that the fumarolic activity was interrupted.

During March-August 1997 seismic activity at Villarrica included 1.5-2.7 Hz tremor and isolated long- period (LP) events associated with phreatic explosions. The latter are common occurrences that have taken place in previous years. Such intervals of elevated seismicity correspond with increased volcanic activity and often include larger amplitude LP earthquake swarms. Although during several days in mid- to late-May 1997 the amplitudes rose to about 20 Real-time Seismic Amplitude Measurement (RSAM) units, around 7 September they reached up to 40 RSAM units and on many days of the month peaks were above 20 RSAM units. Strombolian explosions and night glow were observed between April and August (BGVN 22:08).

Lasting at least eight days, an earthquake swarm during 20-28 October produced RSAM amplitudes an order of magnitude larger than previous months, to >200 units (figure 8). Researchers proposed that October- December swarms may have some seasonal influence associated with higher temperatures in the summer.

Figure 8. Seismic activity at Villarrica during October 1997. The system at the observatory is triaxial with a 1-second period; it was inoperative during mid-October. Courtesy of the Seismological Team, Observatorio Volcanológico de los Andes del Sur (OVDAS).

Escalating seismic amplitudes in March prelude to more explosions and ash

Luis Hernan Ecueñique, a manager in charge of "Las Cavernas," a tourist attraction 8 km from Villarrica's active crater, noted that during late March through at least early April there had been an ascent of magma in the central crater. Erupted material reached ~100 m from the crater's edge. Local tour guides had also informed him that explosions had deposited tephra on the N flanks. Measurements within "Las Cavernas" (which are lava tubes) indicated the air temperature rose by about 2°C.

A digital seismic station 21 km from the crater failed to detect either an increase in the number of seismic events or a shift in their character; the system did register a minor increase in event amplitude.

This report summarizes daily visual observations by members of the Proyecto de Observación Villarrica (POVI), volcano guides, and other sources during February to November 1998. In late February, after two months of subsidence, the magmatic column reached the crater floor with a weak and irregular degassing. By mid-March the lava pond was clearly visible as an intermittent red glow from 12 km away. In April and May, three convective magmatic pushes, gas-poor, filled half of the funnel-shaped crater with pahoehoe lava. On 13, 25, and 30 June, small phreatic emissions rose up to 200 m above the summit. Since mid-October, the activity level in the lava pond has varied, with the low levels of degassing intensity occurring at irregular intervals. On 8 November, the red glow was seen for the only time that month.

It is inferred that the red glow indicates that a small volume of usually gas-enriched magma has reached the crater floor in phases and at irregular intervals. This causes a sudden occurrence of the glow, sometimes with increasing intensity and lasting from a few hours up to 3 days. Subsequently, a distinct reduction of the glow intensity is interpreted to mean that an insufficient supply of convecting magma and gas allows the lava pond to form a crust. During the report period, 16 such magmatic pulses were observed and 10 additional pulses were inferred for periods of non-observation due to weather conditions.

This report summarizes daily visual observations by members of the Proyecto de Observación Villarrica during December 1998 to March 1999. From mid-October through November 1998 team members noted a descent in the lava pond and a drop in visible activity (BGVN 23:11). On 2, 3 and 5 December 1998 a faint red glow was visible above the summit. Afterwards the magma was thought to have reached its lowest level.

When Jürg Alean visited the summit on 21 January, the faint noises caused by degassing could be clearly heard. No recent impacts of bombs were seen in the crater. Early on 5 February, after a break of 2 months, the lava pond reappeared on the crater floor. At about 1300 on 21 February observers saw several dark ash and gas emissions. During 1-26 March the summit remained cloud-covered but apparently little magmatic activity occurred. In the evenings of 29 and 31 March, observers saw glowing pyroclastic material ejected from the crater.

During 1998 the magma column underwent a complete cycle of activity. In January 1998 the column had reached its low; during February-March, the column began slow ascent. From March to September, the column reached hydrostatic equilibrium with its upper surface at the crater floor and this accompanied displays of weak-to-moderate Strombolian eruptions and convective activity in the lava pond. During October-December the column slowly subsided and by January 1999 it again stood at a low level in the vent.

This seasonal sequence has been observed in successive years since 1997 (BGVN 22:04 and 22:08). The seasonal changes in snow and ice mass on the volcano and a well-developed hydrothermal system may affect the magma within the volcanic edifice in a cyclic manner.

The following report, from the scientific team at the Observatorio Volcanologico de Los Andes del Sur (OVDAS), is for the period 20 August through 11 October 1999.

Since 22 August, seismic activity at Villarrica has increased from background levels, shown by an increase in the amplitude of harmonic tremor signals registered at station CVVI, located 19 km from the crater. Periods of high-amplitude tremor lasting 2-30 hours occurred, alternating with background-level tremor (banded tremor). Elevated levels of harmonic tremor lasting for hours-days preceded the last eruption in 1984. OVDAS has therefore recommended to local authorities a move to Level 2 (Green) in the "Semaforo" (traffic light) alert scheme adapted for Villarrica. If the harmonic tremor increases further in amplitude or high levels are maintained for longer periods, recommendations will be made to move to Level 3 (Amber). An energetic long-period event on 15 September, the culmination of this period of high-amplitude tremor, is considered to have been associated with a small explosive event in the crater and ash emission.

The level of seismicity rapidly decreased after 15 September to unusually low levels. Magma level in the crater lake however, is inferred to have been high on 25 September from nighttime observations of glow. Observations by local residents suggest that during the early morning of 26 September a second explosion occurred, depositing new ash. This event was not registered by CVVI so is considered to have been less energetic than the first.

On 1 October, OVDAS scientists on a helicopter flight observed that the level of the magma lake was unusually low (~200 m below the crater rim). The incandescent lava was only visible through a small opening (20-30 m) in a solid crust. Ashfall deposits extended ~5 km ESE from the crater. The deposits clearly exhibited two components, that of the Strombolian fountain (proximally) and that of the upper ash plume. A further increase in tremor amplitude and frequency was observed on 3 October. Observations of new ash and projectiles on the crater rim on the 4th suggested that this tremor episode also culminated in a small explosive event.

A new type of seismic signal, apparently strong hybrid earthquakes, was also registered at the VNVI seismic station (4 km from the crater). They have been increasing in number since 1 October (typically 2-3/day) and are not associated with any visible activity. These events do not comprise the normal background activity.

This report reviews activity during January-May 2000 and September-October 2000. Observations from January through May 2000 were provided by the Proyecto de Observacion Villarrica (POVI). Information about increased seismicity in September and explosions in October were provided by the Observatorio Volcanologico de Los Andes del Sur (OVDAS). Reports for the period June-August 2000 were not available.

Activity during January-May 2000. In January activity was at normal levels. Explosive energy of gas bubbles and incandescence from the lava lake decreased with respect to late 1999. Strombolian activity was observed on 20 January. During February incandescence could be observed on 14 clear nights, indicating weak magmatic activity. Stronger glow was observed on the nights of 19-20 February.

During 1400-1500 on 1 March a series of phreatic events was marked by gas-and-ash emissions. Magmatic activity within the crater decreased with respect to February to more typical levels, causing less incandescence. Activity continued to diminish in April and illumination at the summit also decreased. Incandescence at Villarrica's summit ceased during 5-29 May for the first time since 21 August 1999. At 1430 on 30 May, however, gas-and-ash emissions were observed. Overall, the level of activity was average.

Activity during September-October 2000. As of 20 September, an increase in seismicity occurred at stations VNVI and CVVI while gas and steam emissions ceased, and the usually persistent fumarole disappeared. During 25-28 September, seismic stations VNVI, 4 km from the crater, and CVVI, 19 km from the volcano, recorded anomalous seismicity characterized by clusters of low-frequency earthquakes, harmonic tremor, and tremor bands (periods of tremor separated by seismic silence).

OVDAS raised the hazard status to Green Level 2 on 3 October, indicating that the zone near the crater was dangerous. A flyover of the summit was performed on 4 October to observe any changes in activity. Fumarolic emissions remained absent, and the crater floor was obstructed by black rock. The crater bottom and walls were covered with patches of snow, indicating relatively low temperature. OVDAS prohibited ascents to the top of the volcano because of possible explosions or eruptions. Seismicity that day again showed tremor bands.

On 5 October, an observer of the Centro Volcanológico Villarrica (CVV) reported a short ash eruption with ashfall S towards Coñaripe. At the same time, researchers at the University of Hawaii detected a thermal increase at the summit crater by analysis of GOES 8/10 satellite imagery. Snow fell at the summit on the night of 5 October. An overflight on 6 October revealed a tenuous ash deposit under the recent snow. A small vent opened in the crater, and was subsequently closed by fresh lava. Seismicity included harmonic tremor.

Even a small explosion or eruption would be dangerous because of the potential dislodgement and melting of rock, ice, and snow capping the summit, which could generate a debris flow. Critical locations where lahar risk was highest were determined on the morning of 7 October to prepare for a possible eruption. Crews worked to clear and deepen river channels on or near Villarrica to help reduce damage from a potential lahar. A parapet was also constructed to protect the city and airport of Pucón from debris, ash, or lava flows. Seismicity in the morning showed harmonic tremor, while in the afternoon tremor bands were recorded.

At 1745 on 8 October, a traveler to Coñaripe observed black material rising rhythmically to ~30-50 m above the crater rim and falling back inside. At 1810 there was a small 45-minute-long ash eruption, and wind carried the ash SE. Seismographs indicated harmonic tremor at base levels and at 1400 on 9 October, tremor bands were recorded. An aerial view of the summit on 15 October showed a solid and fractured lava crust on the bottom of the crater and very low gas emission that was mainly water vapor caused by the melting and evaporation of small blocks of ice and snow that fell into the crater. Seismicity remained at a low level as of 15 October.

Since the last report (BGVN 25:10), Villarrica's summit crater continued to be active during October-December 2000.

October 2000 activity. On 18 October the crater bottom lay 70 m below the snow-and-ice-covered summit, it appeared solid and had no visible evidence of disturbance due to underlying fresh lava (figure 9). That night and through the following morning, however, the volcano emitted a small ash-and-gas plume that drifted ENE toward the community of Chinay-Palguín.

Figure 9. Photograph taken during a flight NE of Villarrica's summit crater during the day of 18 October 2000. Note the snow cover and no signs of activity. Photo by Antonio Varas, copyright Sociedad Periodística Araucanía S.A.

On 24 October abundant thermal activity from the crater was observed. Ice and snow that fell from the crater rim down the crater sides and bottom generated enough steam to largely obscure the crater's base (figure 10). When observed on 27 October, the bottom of the crater had increased several meters in height due to outpouring of volatile-poor pahoehoe lava from a small incipient cone and other subsidiary vents (figure 11). Activity consisted of ejection of incandescent material about every 2 minutes, but was not accompanied by degassing sounds. By 30 October, lava had further filled the crater (figure 12, compare to figure 11), but the slow rate of lava discharge prevented the formation of a molten lava lake.

Figure 11. Villarrica's crater rim as seen on 27 October 2000. An incipient cone is visible near the right margin of the crater. The dark vertical patches on the internal wall were caused by melt water. Photo by Enrique Ferrada R., copyright Turismo Trancura.

Figure 12. Villarrica's crater rim as viewed on 30 October 2000. By this time, the outpouring of fluid lava had built up the level of the crater bottom significantly. Comparing features on the back crater wall with those in figure 11 gives a sense of crater bottom growth. Photo by Enrique Ferrada R., copyright Turismo Trancura.

November 2000 activity. The emergent crater bottom reached its maximum height on 1 November (figure 13). Weak incandescence (degree 1 on a scale of 1-5) and ejection of material every ~1-2 minutes could be observed from a point 13 km away that night. By this date the crater was filled with a volume of ~350,000 m3 of material, more than half its capacity. The average effusion rate was estimated to be ~0.45 m3/s during 24 October-1 November.

Figure 13. Villarrica, as viewed from the NW terrace of the crater on 1 November 2000. A pyroclastic cone with little Strombolian activity is visible in the center of the image. Photo by Enrique Ferrada R., copyright Turismo Trancura.

December 2000 activity. Villarrica produced intense showers of lapilli that retextured the crater bottom during 3-5 December; further extrusion of pahoehoe lava filled up the minor depression of a collapse structure. Gas emission decreased, and a lava lake with a thin solidified crust and a 10-m diameter was observed by the end of the interval. Moderate incandescence (degree 3 on a scale of 1-5) and collapse of the cone were observed on 19 December (figure 14).

Figure 14. View of Villarrica's inner crater from the NE on 19 December 2000, showing a large central depression due to collapse, an active vent, and abundant gas discharge. Photo copyright Turismo Trancura and POVI.

Explosive activity. The crater rim was blanketed by abundant ash and lapilli, and on the NW terrace several large bombs and blocks were found, evidencing one or several violent explosions during late 2000 (figure 15). A high risk of explosions remained at the end of the year because lava had grown to such a great height within the crater.

Figure 15. Villarrica's ejecta seen along the crater rim on an undisclosed date in late 2000, with a meter stick for scale. Labeled features are interpreted as follows: 1) a scoriaceous bomb more than 1 m in diameter; 2) a large block whose texture, morphology, and layering suggest that it originated from the crater base, "C" is a dense lithic block that was likely torn from the crater wall; 3 & 4) stratified fragments that originated from the crust that covers the crater bottom. Photos copyright Turismo Trancura and POVI.

At Villarrica during 12-29 January 2001, incandescent lava was observed in the crater and ballistics were ejected ~10-30 m. Frequent explosions occurred, accompanied by degassing sounds that continued through February. During 23-29 March, incandescent lava was observed in the inner walls of the chimney to ~80 m depth. Incandescence was observed in the crater throughout April, and ballistics were ejected ~20-110 m as frequently as every 2-10 minutes during mid-April.

The most outstanding event of 2001 occurred on 14 May at around 1445. An eruption that lasted for 3-5 minutes sent a dark column of particles and gases up to ~1.5 km above the volcano. The eruption was presumably of phreatic origin (triggered by magma-water interaction).

After the eruption, observers continued to monitor Villarrica. This report covers crater visits through early August 2001. In addition, this report presents several years of incandescence and associated air-clarity data.

On 19 June, observers noted few changes in the crater compared to an earlier visit on 24 April. The crater floor contained a large opening, a chimney. Incandescence was observed in the opened upper portion of the sub-vertical chimney. The incandescence appeared along the chimney's ENE edge and could be seen to ~80 m depth. The chimney's cross-sectional form was circular, but on this visit it appeared to have shifted slightly toward the N and had increased in diameter (figure 16). Tephra, including ash (diameter under 2 mm) and lapilli (diameter in the range 2-64 mm), was seen scattered over a large area of Villarrica's snow-covered top, indicating recent outbursts and the potential danger of new explosions. During the visit, no fresh lava emerged at the top of the crater during almost 30 minutes of observation.

Figure 16. Two photos of the floor and lower inner walls of Villarrica's active crater, taken on 4 April and 15 October 2001 from the crater's N rim. In the latter photo the fresh tephra reached 15 m thick. Note the open, sub-vertical chimney disrupting the crater floor. Copyrighted photo courtesy of POVI.

An interest in assessing the position and state of the lava lake from the vantage of an observation post at distance led workers to devise a means to record incandescence. Two indices were devised to describe conditions seen each night, based on qualitative visual estimates made by an observer 13 km to the NW of the crater. The monthly incandescence glow index (Indice de actividad incandescente mensual, IAIM) furnishes a qualitative estimate of incandescence. The monthly visibility index (IVNM) provides a qualitative estimate of atmospheric visibility (air clarity). For both indices, nightly observations assigned values on a scale from 0-5, and these were averaged for each month. The resulting plot shown here accounted for the number of clear nights each month and translated the axis from the index scale to 0-100 percent. Weather and season influence air clarity, the index for which generally ranged between 25 and 100%.

Figure 17 shows an ~4-year record of these estimates. Both indices showed significant variations, but also suggest a particularly strong rise in incandescence during June 2001. Observations on 19 June revealed fluctuations in degassing and brightness that occurred at ~5- to ~10-minute intervals. Observers noted that local ashfalls took place on 20 and 28 June, depositing zones of ash in the summit area.

Figure 17. Qualitative indices of activity at Villarrica during February 1998 through January 2002 based on nightly visual observations from a distance. The histogram records a qualitative estimate of incandescence leaving the crater ("monthly incandescence index"). The line indicates a qualitative estimate of the air's clarity or the visibility ("monthly visibility index"). Larger percentages indicate greater clarity or higher incandescence. Incandescence was judged to be unusually large during June and August-December 2001; crater visits confirmed volcanism around those times. Courtesy POVI.

A report on a 22 July visit stated that both incandescence and the level of the lava surface were low when compared to 19 June. Noise from degassing was weak. A landslide occurred at the inner edge of the central orifice. Although incandescence had decreased earlier, when visited on 9 August strong degassing occurred, and at 60- to 90-second intervals the chimney ejected ash, lapilli, and bombs (up to 20 cm across) toward the W and SW edges of the crater. Similar eruptions occurred on 16, 17, and 21 August. A 22 August visit revealed that the lava lake had risen ~40 m since 9 August.

In August observers on the crater's edge noted an increase in explosive activity, with ballistic heights of 50-150 m. Some scoriaceous bombs had diameters up to 50 cm.

As of October 2001, the rhythmical eruptions seen during the previous 3 months ceased. Material from those eruptions had formed a carpet of tephra that lay scattered around the chimney with thicknesses up to 15 m in the W part of the crater floor. Figure 7 compares the scene in the crater on 4 April to 15 October.

Incandescent lava was observed in the crater during September 2001 through January 2002, and ballistics were ejected ~80-150 m. Explosions generally occurred every ~1-10 minutes and at times degassing sounds were heard.

Our last report described activity at Villarrica during January 2001 (BGVN 27:02) through January 2002, when incandescent lava was observed in the crater and ballistics were ejected ~80-150 m. At that time explosions generally occurred every ~1-10 minutes and degassing sounds were occasionally heard.

During February through at least May 2002, sporadic observations showed a general decrease in activity. Degassing noises were sometimes heard; however, no incandescence or ballistics were reported. A crater visit on 9 April revealed that no incandescence or explosive noises occurred. The surface of the lava lake, last seen on 19 January, remained low (~200 m below the crater rim). On 10 April, explosions occurred every ~10-13 minutes.

The last report of activity at Villarrica, through May 2002 (BGVN 27:06), described a general decrease in incandescence in the summit crater's lava lake, and noted ballistics ejected in January 2002.

Jacques-Marie Bardintzeff reported that climbers to the top of the volcano on 5 November 2004 noted a strong sulfur smell and observed projections of red lava at a depth of 200-300 m in the crater. On 16 November, a small lava lake was visible in the crater from the air; it was photographed on the 19th (figure 18). Many volcanologists attending the IAVCEI General Assembly at Pucón 14-19 November 2004 ascended and observed activity in the summit crater (figure 19). Although the lava lake itself lay at the bottom of a steep-walled inner crater and was not visible, periodic ejection of large quantities of incandescent lava fragments to a maximum height just above the rim of the inner crater could be seen from a bench below the SW rim of the outer summit crater (figure 20). Bardintzeff noted on 24 November 2004 that a white and blue plume of H2O vapor and SO2, extending to the E from Villarrica, was observed from Pucón. During the night, the plume was red colored. According to the local inhabitants, this was the first observation of a plume since January 2004.

Figure 18. A near-vertical aerial view into the ~ 250-m-wide summit crater of Villarrica volcano at about 1430 on 19 November shows the incandescent lava lake in the steep-walled inner crater. The chain of dots left (north) of the crater are climbers near the crater rim. The photograph was taken through the side window of a Cessna aircraft executing an extremely sharp turn. Figure 19 (below) was taken from the upper left crater rim and figure 20 from the lower right. Courtesy of Jean-Claude Tanguy.

Figure 19. Climbers walk along the outer snow-covered rim of Villarrica's summit crater on 17 November 2004 and stand on a small bench just below the SW rim (left), which provided periodic views of incandescent ejecta from the inner crater lava lake (figure 20). Courtesy of Judy Harden.

Figure 20. Incandescent spatter and bombs are ejected from the lava lake in the inner crater of Villarrica as seen from a bench just below the SW rim of the outer crater on 17 November 2004. Courtesy of Judy Harden.

According to the Publicación Oficial del Grupo Projecto de Observación Villarrica (P.O.V.I.) website, incandescence was seen above the summit crater on the nights of 5-6 August and 27-28 October 2004 and frequently during November and December. On the night of 12-13 December Strombolian explosions every 2-5 minutes ejected incandescent spatter and bombs to 100 m height that landed on the outer crater rim. On the 13th the lava lake was ~ 30 m in diameter and at a depth of ~ 100 m. Vigorous convection of the lava lake was punctuated at intervals not exceeding 15 seconds by Strombolian explosions that ejected fine ash, lapilli up to 4 mm in diameter that fell to within a few meters of the inner edge of the crater, and incandescent spatter to the NE to heights of ~ 50 m. By 27 December solidification of ejected spatter around the vent had decreased its diameter by 2/3 with respect to 13 December, and Strombolian explosions at intervals of 2-5 minutes ejected material ~ 100 m above the vent. On 9 and 17 January minor explosions took place at intervals of 1-2 minutes. By 17 January fissures had formed around the N to E sides of the vent, and the opposite side of the vent edge, and the slope above it, had collapsed.

Satellite-based MODIS thermal alerts were first detected at 0345 UTC on 5 November and also occurred on 6, 16, 17, 22, 24, and 29 November, 5, 8, 9, 14, 19, 21, and 31 December, and 1 and 2 January 2005. Prior to 5 November 2004, MODIS thermal alerts not previously reported in this Bulletin had been detected at Villarrica on 23 May, 10 and 17 July, 2, 6, 25, and 27 August, 16 and 28 September, 2, 12, 14, 27, and 30 October, 1, 3, 22, and 28 November 2003, 31 January, 1-3, 7, 10, 12, and 14 February, and 0345 UTC on 26 March 2004 (2345 local time 25 March). According to the P.O.V.I. website, strong explosive activity ejected incandescent pyroclastic material on 28 August 2003, and except for three cloud-covered days, incandescence above the summit crater was seen daily from 27 January to 20 February 2004.

Our last report on Villarrica, through January 2005, described plumes, the growth of a lava lake in the crater, and some night-time Strombolian explosions (BGVN 29:12). This report covers January to April 2005.

According to the March 2005 newsletter of the Multinational Andean Project: Geoscience for Andean Communities (MAP-GAC) produced by the Geological Survey of Canada, both seismic activity and degassing from the permanent fumarole increased in January. One of the early January explosions described above sent pyroclastic material (ash and scoriaceous lapilli) onto the flanks of the snow-and-ice covered volcano, covering an area 1 km wide and 3 km long. Subsequent minor explosions have sent pyroclastic material to estimated heights of 300 m above the crater. Onlookers have reported incandescent material within the gas-and-pyroclastic column.

On 19 January 2005, volcanologists Hugo Moreno and Edmundo Polanco of OVDAS–SERNAGEOMIN observed the lava lake actively spattering at a distance of 30 m below the edge of the principal crater; the crater interior and perimeter were covered in spatter. The glacier covering the cone had developed new fractures and crevasses. Activity in February 2005 lessened.

During 29 March to 3 April 2005, the lava lake inside Villarrica's crater remained active, with Strombolian explosions occurring. Some gas explosions were observed to hurl volcanic bombs as far as ~ 300 m. According to a news report on 12 April 2005, the Oficina Nacional de Emergencia reported that unusual seismicity was recorded at Villarrica during early April. Fresh ash deposits were seen outside of the volcano's crater. Visitors were banned from climbing the volcano.

During 29 March to 3 April 2005, the lava lake inside Villarrica's crater remained active, with Strombolian explosions occurring. Some gas explosions were observed to hurl volcanic bombs as far as ~ 300 m. According to a news report, the Oficina Nacional de Emergencia reported that unusual seismicity was recorded during early April 2005. Fresh ash deposits were seen outside of the crater. Visitors were banned from climbing the volcano.

Since the beginning of 2005, relatively consistent and continuous MODIS/MODVOLC thermal anomalies were recorded during 1 January through 25 March, 7-21 July, 31 August through 26 September, 17 October through 25 December 2005, and 23 January through 4 September 2006 (figure 21). The gaps between these periods are probably artificial, due to such interference as cloud cover or other phenomena that obscured satellite observations. For example, the activity reported above for late March through early April 2005 did not generate MODIS/MODVOLC thermal anomalies.

Figure 21. Thermal anomalies at Villarrica from the MODIS/MODVOLC satellite observations, January 2005 to 18 September 2006. Anomalies are from both the Aqua and Terra satellites. Courtesy of the HIGP MODIS Thermal Alert System.

Thermal anomalies throughout 2007; ash plumes November 2007 and October 2008

Our last report on Villarrica (BGVN31:08) discussed the nearly continuous thermal anomalies between 1 January 2005 through 4 September 2006. This report updates this information through 10 February 2009 and suggests ongoing activity from the lava lake inside Villarrica's small, deep summit crater. Seismic and textural insights on the volcano are discussed by Gurioli and others (2008).

MODVOLC thermal alerts were issued nearly continuously during September 2006. Alerts then followed during 26 October 2006 through 18 February 2007, during 29 April 2007 through 5 June 2007, during 9-11 July 2007, and during 6 September 2007 through 25 December 2007 (24 December local time). The gaps between these periods may be due to cloud cover or other phenomena that obscured satellite observations.

From 26 December 2007 to as late as 10 February 2009, only two thermal anomalies were detected. One (MODIS) was on 2 June 2008, the other (ASTER) on 25 June 2008.

Villarrica has been relatively quiet since 4 September 2006. However, there have been reports of minor activity. According to the the Buenos Aires Volcanic Ash Advisory Center (VAAC), on 14 November 2007 an eruption plume rose to an altitude of 3.8 km and drifted E. Ash was not detected on satellite imagery.

On 26 October 2008, according to the Observatorio Volcanológico de los Andes del Sur-Servico Nacional de Geologia y Mineria (SERNAGEOMIN), three gray plumes containing a small amount of ash were discharged from the main crater and rose 100 m above the crater rim. These plumes quickly dispersed E. A fourth and larger darker gray plume rose 200 m above the crater rim and, according to the Projecto Observación Visual Volcán Villarrica (POVI), deposited a thin layer of tephra several kilometers long on the E flank. Incandescence was not detected.

A SERNAGEOMIN report on 30 October 2008 characterized seismic activity during the previous several months as weak background tremor and small earthquakes. The report commented that this seismicity might be caused by shallow degassing in the main conduit, glacial melting increasing the volume of water in the hydrothermal systemand causing explosions, or conduit obstructions.

Villarrica has been relatively quiet since 4 September 2006. However, there were reports of minor activity, with occasional ash plumes and thermal anomalies through 10 February 2009 (BGVN 34:01). According to the Observatorio Volcanológico de los Andes (OVDAS-SERNAGEOMIN), during February 2009 through February 2010, the volcano experienced frequent tremor and occasional long-period earthquakes, with infrequent tectonic and hybrid earthquakes. Persistent Strombolian activity, with frequent detection of thermal anomalies, began in April 2010.

Photographs and video posted on the Projecto Observación Visual Volcán Villarrica (POVI) website demonstrate weak fumarolic activity during January-March, September, and December 2009. Climbers also documented diffuse gas plumes rising from the crater in early 2009 (figures 22 and 23). Fumaroles may have been active during other months as well; according to POVI, such emissions are a recurrent phenomenon at Villarrica, especially during times of thaw. The POVI photos and captions specifically noted that there was a phreatomagmatic explosion on 29 January. A small ash plume seen on 19 March was due to small collapses within the crater. A pyroclastic flow deposit was photographed on the upper NE flank on 22 November. Observations during an overflight on 11 December showed bombs and ashfall near the crater rim.

Figure 22. Photo of Villarrica's crater on 25 February 2009, with a diffuse gas plume rising from the central pit. Visitors can be seen on the far crater rim, where some snow is present. View is towards the NNE, with Llaima in the distance. Courtesy of Szymon Kochanski (Creative Commons license).

Figure 23. Photo showing the cone of Villarrica during an ascent on 8 March 2009. A very diffuse fumarolic plume is rising from the crater, which appears snow-free near the summit. Courtesy of James Byrum (Creative Commons license).

Visitors in January 2010 recorded similar degassing conditions (figure 24) as that often seen in 2009. According to a January 2010 report by OVDAS, the only part of the crater that showed signs of heat without the presence of fresh snow was a fumarole on the SE margin of the crater. On 1 January 2010, the POVI webcam imaged a dark low-altitude plume. Incandescence was seen at night during January and February. According to the Buenos Aires Volcanic Ash Advisory Center, on 11 March a diffuse gas-and-ash plume drifted near the crater; ash was not detected on satellite imagery. OVDAS reported that, during an overflight, scientists saw a typical-looking gas plume drifting SW that day and tephra deposits on the flanks.

Figure 24. Photo of Villarrica's crater on 24 January 2010. A diffuse gas plume is rising from the crater (left). View is from the N crater rim. Courtesy of Liam and Hels (Creative Commons license).

On 24 March, the webcam recorded steam emanating from the crater; the steam was caused by the heating and then condensation of snow from a recent storm. In April, seismic activity increased somewhat, accompanied by a rise in the lava lake level, more vigorous fumarolic activity, and more frequent incandescence at night. Strombolian activity was seen by climbers on the crater rim on 23 April (figure 25). Additional videos and photographs taken during 24-25 April, and 8 and 10 May (posted on the POVI website) showed continuing Strombolian activity in the crater. Bursts of lava did not rise above the crater rim, but gas plumes rose from the crater. The increased activity prompted OVDAS to increase the Alert Level from Green Level 1 to Green Level 2. According to POVI, on 10 May the spattering lava lake was about 100 m below the crater rim.

Figure 25. Photo of Strombolian activity in Villarrica's crater taken on 23 April 2010. Courtesy of elrentalplats (Creative Commons license).

During 2009 thermal anomalies detected using MODIS/MODVOLC data occurred on 24 March, 9 April, and 26 November. An ASTER image also showed an anomaly on 8 March 2009. Detection of thermal anomalies continued in early 2010, with hot spots on 6 and 22 January, 10, 14, 16, and 23-26 February, and 11 March. Beginning on 5 April 2010, thermal anomalies became more frequent, with detections on 18 days in April, and 14 days in May.

During April-October 2010, nearly continuous gas plumes from Villarrica (figures 26 and 27), sometimes containing small amounts of ash, occasionally rose higher than 700 m above the crater rim. Tremor occurred, as well as frequent incandescence at night. During that time, there were 118 thermal alerts derived from the Hawai'i Institute of Geophysics and Planetology Thermal Alerts System (MODVOLC). Activity through April 2010 consisted of steam emanating from the crater punctuated by periods of Strombolian activity from the lava lake, which has been observed in the majority of eruptions since 1996; however, bursts of lava did not rise above the crater rim (BGVN 35:04).

During April, Observatorio Volcanológico de los Andes del Sur-Servico Nacional de Geologia y Mineria (OVDAS-SERNAGEOMIN) reported that the level of the lava lake rose slightly, gas emissions increased, and incandescence at night was more frequent. Seismicity also increased, with a total of 165 seismic events, of which 158 were tremors. The Alert Level was raised from "Green Level 1" to "Green Level 2" (out of a 3-color, 8-level scale). On 10 May, the surface of the spattering lava lake was ~100 m below the crater rim.

There was a slight increase in volcanic tremor through June, with a gradual decline after 26 June. Around this time, OVDAS-SERNAGEOMIN suggested that an unspecified decrease in the height of the lava lake was related to this decline in seismicity. From 9-22 July, tremor detected by the VN2 seismic station, 4 km NW of the summit, increased (figure 26). The events were located at depths of 6-10 km below the summit, except two that occurred 6 km S of the crater.

Throughout August 2010, most of the 485 seismic events recorded were long period; the largest of which was an M 2.1 located on the E edge of the caldera. During 13-15 August, slight increases in seismicity were correlated with increases in the shape and height of the steam plume emitted from the summit crater.

Seismicity decreased during September 2010, with a total of 161 seismic events recorded. On 4 September, a diffuse ash plume, possibly containing steam and gas, drifted NE. Seismicity increased significantly in October, totaling 1,874 long-period events. According to Projecto Observación Visual (POVI), ash plumes observed on 10 and 24 October and 1-2 November rose to altitudes of 3.7-4.6 km and drifted NE.

During November 2010 to December 2013, lava lake persists but few explosions

The year 2014 marks the 3rd decade of largely non-explosive activity at Villarrica, historically one of the most active volcanoes in the Andes. Villarrica has been relatively quiet since our last report, which discussed events from April 2010 to October 2010 (BGVN 35:10). This report covers the time period from November 2010 to December 2013.

During this reporting period, comparative quiet prevailed. There were occasional cases reported of spattering lava, small white plumes, minor ash emissions (up to 50 m above the crater rim), and nighttime incandescence reflected off of the plumes according to Proyecto Observación Villarrica Internet (POVI) and Observatorio Volcanológico de los Andes del Sur (OVDAS-SERNAGEOMIN). Satellite thermal radiance during the reporting interval suggested often low radiance, with rare cases of high incandescence consistent with turbulence and fountaining in the deep, 40 m wide lava lake.

On 17 September 2011 remobilized tephra rose ~500 m above the crater, which according to POVI, was likely caused by a sudden impact when a snow cornice detached and fell into the crater. On 19 September 2011, a rapid rise in the level of the lava lake caused much of the snow and ice to melt, especially on the southern inner wall. Strombolian explosions from the crater were observed on 26 September 2011, and tephra deposits on the E edge of the crater were noted. On 27 September 2011 incandescence from the lava lake was reflected in the cloud cover above.

The period from November 2011 to March 2012 saw very little explosive activity. Two small ash emissions occurred on 7 March. Incandescence from the crater was observed from the town of Pucon (16 km N) during 7-8 March. During 7-9 March, lava spattering from the lava lake was observed for the first time that year. Four small ash emissions were observed during 13-14 March. On 20 March a large, white plume was visible above the crater. The observer postulated that due to the humid atmospheric conditions that day, the steam condensate in the visible plume remained conspicuous both to a height of 1,500 m above the crater as well as 20 km SW of the crater.

According to POVI, an ash plume rose 50 m above Villarrica on 19 April 2012. Incandescence from Villarrica's crater subsided in mid-April and was undetected by satellite and ground observations at least through 10 November 2012.

On 30 January 2013, weak incandescence was observed in the near-infrared spectrum from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument on the Terra satellite. POVI reported that satellite images of Villarrica acquired on 25 July revealed a weak thermal anomaly. On 29 July 2013 observers photographed the crater and described a thermal anomaly on the S edge of the crater rim, in the same area from which a lava flow originated on 29 December 1971. They also heard deep degassing sounds. A second photograph showed a diffuse gas plume rising from the bottom of the crater, and ash and lapilli on the snow on the inner crater walls.

Analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) band 21 (3.929-3.989 μm) satellite images from 2003 to 2013 highlights three main cycles of activity. These were characterized by convective lava fountains and Strombolian explosions from the lava pit, located ~ 40-150 m below the rim of the crater, according to POVI. The last time MODIS infrared sensors detected elevated thermal radiance was in early 2012 (figure 8).

Figure 28. Elevated thermal radiance in Watts per square meter detected at Villarrica using MODIS band 21 (3.929-3.989 μm) from 2003 through 2013. Courtesy of POVI and NASA MODIS.

In accord with the thermal radiance data seen in figure 28, OVDAS-SERNAGEOMIN maintained an Alert Level of Green for Villarrica from the period of 5 March 2012 to 30 December 2013, characterizing Villarrica as active but stable with no immediate threat. The seismicity reports from OVDAS-SERNAGEOMIN during the period of July 2013 to December 2013 showed the monthly number of earthquakes recorded ranged from 439 to 1,433. The reduced displacement of the tremors recorded fluctuated throughout July 2013- December 2013 from 0.6 cm² to 9.9 cm². During this period of time, the amount of SO2 emissions recorded by a scanning DOAS spectrometer OVDAS-SERNAGEOMIN varied from 156 tons/day to 888 tons/day. The height above the crater rim of the steam-gas plumes ranged from 150 m to 1,500 m. MODIS did not record any thermal anomalies during this period of time.

Figure 29. Aerial image of the Villarrica crater at dawn on 14 October 2013. Copyrighted image taken by Diego Spatafore.

Lava lake reappears in February 2015 and is ongoing; large ash explosion on 3 March 2015

Villarrica is a stratovolcano located 675 km S of Santiago, Chile. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently visible lava lake with Strombolian activity was responsible for persistent MODIS thermal anomalies between November 2009 and April 2012. Very little additional activity was observed until December 2014, when renewed activity was reported by the Southern Andes Volcano Observatory, (Observatorio Volcanológico de Los Andes del Sur, OVDAS) part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), a privately funded research group that studies Villarrica.

Increased fumarolic and thermal activity was first observed in early December 2014 followed by Strombolian activity and ash emissions during 4-6 February 2015. A large explosion with an ash plume to 9 km altitude took place on 3 March 2015, and continued moderate explosive and Strombolian activity occurred a number of times during March. Explosive activity with ash plumes and lava spattering continued at decreasing levels throughout 2015; in 2016, minor ash emissions were only reported in September. Intermittent Strombolian activity at the lava lake occurred throughout 2015 and 2016 and was recorded as significant thermal anomalies through October 2016.

Activity during 2014. OVDAS reported that seismic activity in 2014 started the year very low with 604 total events in January. Steam plumes remained below 500 m above the summit throughout the year except for one report of heights to 800 m in February. Tremor displacements in 2014 remained in the range of 0.4 to 1.2 cm2 at frequencies of 1.1-1.2 Hz and amplitudes of 0.6-0.7 μm/s, all within background levels. Sulfur dioxide emission values ranged between 180 and 566 metric tons per day (t/d) as monthly averages, with maximum values not over 1,600 t/d throughout the year. The number of seismic events increased from 1,160 in April to 3,269 in May 2014, and took a larger jump between June and July from 4,268 to 11,031. The number of monthly seismic events remained in the 10,000-12,000 range through 2014, while the other parameters measured by OVDAS remained stable. There were no reported ash emissions.

As a privately funded research group, POVI documents activity at the volcano with webcams, photographs, and frequent summit ascents. They first observed increased sulfurous fumarolic activity on 25 November 2014. They also reported on NASA ASTER IR observations of a progressive increase in spectral brightness in satellite data on 10 and 26 November and 3 December. POVI observed the presence of particulate matter suspended over Villarrica on 9 December, and a light dusting of material within 1,000 m of the summit the following day. Increased acoustic activity of loud explosions of gases inside the 40-m-wide volcanic vent at the summit crater were reported during 10-12 December.

OVDAS reported on 18 December 2014 that the seismic energy had abruptly declined on 9 December. A flyover by the Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), the National Emergency Office of the Ministry of Interior and Public Safety, on 17 December was not able to observe the bottom of the crater due to weather conditions. In January 2015 seismic activity returned to previous levels and other measurements remained at background levels.

Activity during 2015. On 4 and 5 February 2015 POVI observed the first Strombolian eruptions inside of the summit crater vent since April 2012, and constant strong degassing occurring in 10 minute pulses. On 6 February they captured nighttime images of incandescent explosions rising to 65 m above the crater edge. Spatter fragments up to 40 cm were scattered around the summit. POVI also recorded two ash explosions on 6 February, and photographed 5 m diameter incandescent blocks on 7 February in the air 45 m above the crater.

A gradual increase in the amplitude of the seismic tremor signal was reported by OVDAS beginning on 6 February. The seismic signal rose from DR (Reduced Displacement) values of 4.0 cm2 to 24 cm2, and amplitudes increased to 18.5 μm/s, considered moderate to high for Villarrica and significantly above its background values of 2 cm2 and 1 μm/s. The location of the tremor signal was also shallower than it had been previously.

During the night of 9-10 February, POVI observed about 24 Strombolian explosions that rose above the crater rim and sent large blocks several meters down the NW flank. MODVOLC thermal anomalies pixels first reappeared on 14 February 2015. Between 14 and 16 February two active lava lakes were observed by POVI within the summit crater in nighttime imagery and during a flyover. OVDAS reported up to five explosions per minute at the summit crater on 16 February and continued nighttime incandescence since 6 February accompanied by intermittent ash emissions. Ejecta on 16 February was observed up to 1 km away on the S flank. Temperatures close to 800°C were measured that day near the lava lake surface on a flyover supported by ONEMI; tephra was observed around the crater rim and a thin layer of ash was distributed on the flanks. This caused SERNAGEOMIN to raise the alert level from Green to Yellow (1 to 2) on a 4-level scale.

A further increase in seismic energy release was reported by OVDAS on 28 February 2015 with DR values increased to 35 cm2, along with observations of nighttime incandescence and Strombolian explosions ejecting tephra up to 1 km from the crater. Two days later SERNAGEOMIN raised the alert level to Orange (3 of 4) based on increased DR values close to 80 cm2 and seismic amplitudes of 40 μm/s, as well as increased Strombolian activity and bombs ejected to 500-600 m from the crater.

An explosion early in the morning of 3 March 2015 with a 3-km-high ash plume, DR values near 400 cm2, and seismic amplitudes of 1,400 μm/s prompted SERNAGEOMIN to raise the alert level to Red (4 of 4) that morning. They reported observations from cameras around the volcano of a 1.5-km-tall lava fountain (figure 30). The Buenos Aires VAAC (Volcanic Ash Advisory Center) reported a plume to 9.1 km altitude drifting ESE later in the day. Significant ashfall was also visible around the flanks shortly after the explosion (figure 31).

Figure 30. Explosive eruption at Villarrica on 3 March 2015, photographed from the city of Villarrica, 30 km NW of the volcano. The lava fountain was reported as 1.5 km tall. Courtesy of POVI.

Figure 31. Ground-based webcam and satellite views of Villarrica before and after the 3 March 2015 eruption. The ash plume drifted E and spread ash on the glaciers around the N and E flanks of the volcano. The explosion sent ejecta radially outwards generating small lahars in drainages to the north and east. Images A and B courtesy of POVI (copyright by Mario Alarcon N.) from a camera located in Pucón, 17 km N. Images C and D annotated by POVI; courtesy of NASA Earth Observatory.

The alert level was lowered back to Orange (3 of 4) on 6 March 2015 as activity decreased. During a flyover on 9 March, OVDAS scientists observed that the vent inside the crater was partially obstructed with debris, and fumarolic activity was weak. Minor debris avalanches had significantly decreased and the alert level was lowered to Yellow (2 of 4) on 10 March. A minor ash emission, under 100 m above the crater, occurred on 15 March. Two weak Strombolian explosions to 150 m above the crater were reported by OVDAS on 17 March. During 17-18 March, continued explosions with volcanic bombs, incandescence, and fine ash caused SERNAGEOMIN to raise the alert level back to Orange. POVI observed ash drifting E less than 70 m above the crater during this time.

The Buenos Aires VAAC reported water vapor and light ash emissions to 3 km beginning 22 March, drifting 45 km SE and continuing intermittently through 25 March. OVDAS reported sporadic incandescence throughout this time and intermittent ash plumes generally 100-500 m above the crater. POVI had also noted pulsating emissions of fine ash during 18-25 March. A significant increase in activity on 25 March led to a 700-m-high plume with high ash content, and visible incandescence. A flyover by OVDAS/ONEMI that day confirmed the presence of the lava lake near the surface again with temperatures around 1,000°C. The Buenos Aires VAAC reported a 5.5-km-high ash plume on 27 March extending 55 km NE. Plume heights exceeded 800 m on 28 March, with ejecta from the lava lake landing around the summit and upper flanks, and night incandescence. Strombolian explosions were observed for most of the night on 30 March. The highest explosion of spatter reached 300 m above the crater, and material fell 500 m away onto the flanks. That same day the Buenos Aires VAAC reported continuous ash emissions with a plume to 3.7 km drifting NE. On 31 March they reported irregular intermittent water vapor with small puffs of ash that were observed on the OVDAS web camera.

Strombolian activity fluctuated during April 2015. Pulsating emissions of water vapor were common. OVDAS reported ash plumes to 700 m above the summit crater on 4-5 and 20-21 April but otherwise periodic ash plumes were below 500 m. Buenos Aires VAAC reported the 5 April ash plume rising to 3.7 km altitude and drifting 16 km SSE. Ejecta occasionally reached 200 m from the crater. Nighttime incandescence from the crater was usually observed during clear weather, and seismicity generally decreased during the month. The lava lake and the formation of an incipient pyroclastic cone inside the inner crater were observed in an OVDAS/ONEMI flyover on 9 April; on a 21 April flight moderate Strombolian activity was viewed restricted to the interior of the crater.

During May 2015, OVDAS reported small Strombolian explosions from the lava lake, diffuse gas emissions with occasional ash, nighttime crater incandescence, and decreasing seismicity. Activity continued to gradually decline, and on 8 June the Alert Level was lowered to Yellow.

Sporadic incandescence was still observed during clear weather between June and September 2015, with plume heights below 450 m except for occasional plumes to 700 m above the summit crater. Two ash emissions were recorded on the OVDAS cameras on 18 and 21 September to heights less than 400 m. Plume heights in October were near 700 m, and another small ash emission was recorded on 31 October along with incandescence on clear nights. A group of OVDAS scientists conducted a field visit on 27 October and observed 11 new small fumaroles on the inner wall of the crater, and steep walls of pyroclastic material generated in the explosions from earlier in the year. They observed the lava lake in an overflight on 29 October and the temperature of the lake was measured at 850°C (figure 32). During the second week of November weak explosions were heard and pyroclastic material was observed above the crater rim; plume heights were close to 400 m, but rose to 700 m in December. A particulate emission that rose to 200 m above the crater occurred on 15 December. SERNAGEOMIN lowered the alert level to Green on 31 December 2015.

Although ash emissions and Strombolian activity were intermittent and generally decreasing after June 2015, strong thermal anomalies seen in MODVOLC data continued throughout the year. February, March, July, August, October, and November each had between 5 and 10 days with thermal anomalies while April, May, June, September, and December all had between 10 and 15 days with MODVOLC alert pixels, indicating continued activity at the lava lake.

Activity during 2016. Water vapor plumes rose to 600 m above the crater in January and February 2016, along with slightly increased SO2 emissions and night incandescence. Small ash emissions on 6 and 29 February and the formation of a small pyroclastic cone inside the crater were observed by visiting scientists from the University of Cambridge. One VT (volcano-tectonic) earthquake of M 3.7, larger than normal, was reported by OVDAS on 26 March; it was located 4.7 km ESE of the crater at a depth of 4.2 km. This was followed by a spike in the number of VT events the following day. The amplitude and frequency values associated with seismic tremors remained within normal levels until a sudden but brief increase on 3 April that was associated with explosions and minor Strombolian activity at the lava lake within the crater. This activity resulted in SERNAGEOMIN raising the alert level to Yellow. The frequency of clusters of VT seismic events increased during the second week in April; most were located in a NW-SE trending belt about 10 km long near the crater vent. Water vapor plumes continued rising to around 600-700 m above the crater during April and May with no significant changes in incandescence. OVDAS reported small emissions of particulate material around the crater in April and on 4 May. The alert level was lowered back to Green on 16 May.

From May through July 2016, only water vapor plumes between 300 and 700 m above the summit were reported by OVDAS. August was quieter still with plumes rising to only 150 m. Seismicity increased slightly in September, plumes rose to 600 m, and on four days (5, 10, 19, 24) small emissions of ash were observed. Water vapor plumes remained below 700 m in October, 2016.

While significant explosive activity did not occur during the year through October 2016, the lava lake remained visible and active, causing thermal anomalies recorded by MODIS and measured by both the MODVOLC and MIROVA systems. MODVOLC recorded thermal anomalies between 5 and 10 times each month from January through April, between 1 and 4 times in May, July, and August, and again between 5 and 10 times in September and October. This variation is also reflected in the MIROVA Log Radiation Power graph for 2016 (figure 33).

Figure 33. MIROVA system Log Radiative Power data for Villarrica between 8 November 2015 and 8 November 2016. The thermal anomalies were continuous and consistent except for a quiet period between late May and early August 2016. Courtesy of MIROVA.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Villa Rica | Quitralpillan | Pucon | Pucanu

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Huichatio

Vent

Craters

Feature Name

Feature Type

Elevation

Latitude

Longitude

Llafenco Group

Crater

Pimenton

Crater

Basic Data

Volcano Number

Last Known Eruption

Elevation

LatitudeLongitude

357120

2017 CE

2847 m / 9338 ft

39.42°S
71.93°W

Volcano Types

Stratovolcano
Caldera(s)
Pyroclastic cone(s)
Fissure vent(s)

Rock Types

MajorBasalt / Picro-Basalt
Andesite / Basaltic Andesite
Rhyolite

Tectonic Setting

Subduction zoneContinental crust (> 25 km)

Population

Within 5 kmWithin 10 kmWithin 30 kmWithin 100 km

477
1,067
35,118
667,788

Geological Summary

Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Photo Gallery

Snow-capped Villarrica, one of Chile's most active volcanoes, is seen here in 1984 with a dark-colored lava flow descending its flank. Plinian eruptions and pyroclastic flows have been produced during the Holocene from this dominantly basaltic volcano, but historical eruptions have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Lahars from the glacier-covered volcano have damaged towns on its flanks.

Photo by Hugo Moreno, 1984 (University of Chile).

A lava flow descends the NE flank of Villarrica volcano in 1984. A small lava lake at the NNE side of the summit crater fed lava flows through a notch in the crater rim left by the 1971 eruption. The lava initially flowed down the summit icefield and then burrowed under the glacier. The flow emerged onto the surface on November 13, producing a 3-km-long avalanche of lava blocks, ice, and snow.

Photo by Hugo Moreno, 1984 (University of Chile).

A dark lava flow descends the Chaillupén river on the SW flank of Villarrica volcano towards Lake Calafquén during an eruption in 1971. The lava flow overrides light-colored mudflow deposits produced earlier during the eruption, which began on October 29. On November 29 lava effusion and pyroclastic cone formation began. Three basaltic lava flows were emitted on the SW flank during December 3-20. The eruption culminated on December 29, when lava flows melted ice, producing lahars that swept the volcano's flanks and caused 15 fatalites. The eruption lasted until January 10.

Photo by Hugo Moreno, 1971 (University of Chile).

Snow-covered Villarrica, one of Chile's most active volcanoes, rises above the resort town of Pucón below its northern flank. A faint steam plume drifts from an active lava lake in the summit crater. The steep summit cone was constructed within a mostly buried, 2-km-wide caldera whose dissected outer flanks rise above the tree line. Villarrica is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. Historical eruptions have been documented since 1558 CE.

Phot by Lee Siebert, 2004 (Smithsonian Institution).

Incandescent spatter and bombs ejected from a lava lake at the bottom of a steep-sided, ~40-m-wide inner crater are seen from the SW rim of Villarrica's outer crater on November 19, 2004. Incandescence was seen above the summit crater the nights of August 5-6 and October 27-28, 2004 and frequently during November and December. Strombolian explosions ejected material to 100 m the night of December 12-13. Ground observations of summit lava lake activity and minor strombolian explosions were continued into 2006.

Photo by Lee Siebert, 2004 (Smithsonian Institution).

A near-vertical aerial view into the ~250-m-wide summit crater of Villarrica volcano on November 19, 2004 shows an incandescent lava lake in the steep-walled inner crater. The chain of dots left (north) of the crater are climbers near the crater rim. Night-time glow was periodically visible from the town of Pucón on the north flank of volcano beginning in August 2004 and intensified in November and December. Small strombolian explosions in December ejected spatter and bombs onto the crater rim.

Affiliated Sites

The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the MAGA Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO2 to the atmosphere, but installing CO2 monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).